×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Essential-Service Motor Defeating some important motor protection ?
4

Essential-Service Motor Defeating some important motor protection ?

Essential-Service Motor Defeating some important motor protection ?

(OP)
Hello every body,

I have problems with my motor protection lots of them, often false tripping and no cause found try hundred times to to trouble shot or probably incorrect settings but everything seem OK.
When I  found technical paper from GE chapter 10 A-C Generator and motor protection on page 202 its rather confuse me its seem the motor is poorly protected, is it a usual pratice ?

If I want to disable the 46 that protect motor from single phasing trip, is there someone can advise me the brand that sell single function 46 device (the relay I got is one package) or is it safe enough and leave it to thermal as back up?

RE: Essential-Service Motor Defeating some important motor protection ?

You are dealing with the age-old quandary of a short-term fix versus longer-term cure.  

Disabling of a protective function needs careful review, understanding and acceptance by your management.  Up the ladder a bit, production management will at times be at odds with maintenance management over preventive and breakdown repair efforts.

Remember that single phasing and phase loss are extreme cases of phase imbalance.  A lot of stator damage can occur with less than a simple open phase.  Thermal-overload relays (or their numerical equivalent) are generally much less sensitive to imbalance conditions and their consequences.  

The 46 device is a negative-sequence current relay that is sensitive to current imbalance.  Insulation failure from excess-heat generation in the stator can easily lead to serious repair costs and loss of production.   Consider removal / transport / reinstall labor and motor-shop expenses -– possibly at a premium overtime rate.
  
Clearly understand system and component operating sequence.  What external mechanical and electrical conditions influence electrical characteristics the relay is measuring?   Is there an event report that the multifunction protective device can furnish?   At what level were settings determined -- in-house or by an outside engineering firm?  Are you able to verify that the intended settings are indeed programmed into the protective device?  Can the protective relay package be tested removed from normal service?  At some point, instrument-transformer and other control wiring needs careful verification.

It may be time to contemplate retaining some outside help or test equipment rental.  Weigh using a multisource protective relay set versus a simple OL relay test box; i.e., primary versus secondary injection.  An apparatus-repair or electrical-testing firm should have some track record with the particular protection package at hand.

These are some valid questions for what can be a very frustrating situation; that is, being under pressure to quickly and reliably troubleshoot a problem that is causing immediate production losses.  The term “essential-service motor” should not be taken lightly.  Bet on this being a good learning experience.

RE: Essential-Service Motor Defeating some important motor protection ?

(OP)
Busbar I give you astar there.
We already invite the relay vendor to site and they bring some fancy test equipment and still cannot find whats wrong with their relays.
Our manager already tired dicking around the vendor and think to buy some very standard motor protection and not to use this relays on our next project.

RE: Essential-Service Motor Defeating some important motor protection ?

One standalone relay is a Basler Electric BE1-46N.  It has optional analog output proportional to AC negative-sequence current.  

RE: Essential-Service Motor Defeating some important motor protection ?

Suggestion: Reference:
1. ANSI/IEEE Std 242-1986 "An American National Standard IEEE Recommended Practice for Protection of Industrial and Commercial Power Systems"
1)Reference 1 page 148 par 4.8 "Phase Balance Current Relay - Device No. 46" indicates two different kinds of 46:
1a) Current balanced relay that operates when the difference in the magnitude of rms currents in two phases exceeds a given percentage value. This one will leave you some margins to consider.
1b) The negative sequence current relay operates on magnitude of negative sequence current, but is calibrated in terms of (I2**2)xt, the thermal energy produced by the negative sequence current. In order to set the negative sequence relay, the (I2**2)xt characteristic of the machine must be specified. This is not addressed in the above postings. The solid state 46Negative provides an alarm at sensitive pretrip value of (I2**2)xt in addition to the trip setting.
2. Normally, the phase unbalance protection is applied to motors 1000hp and up.
3. If you consider any delay in motor trip, e.g. 2 or 3 seconds, the motor designer should be contacted.
4. Reference 1, Section 9 "Motor Protection" practices are recommended. Notice that 46 Phase Current Balance may have inherent time delay. 46 Negative-sequence voltage operates instantaneously and may need timer. 46 Negative-sequence current is not intended for motors since it has a relatively high pick up. This statement cautions to use any unsubstantiated recommendation as far as this relay is concerned.

RE: Essential-Service Motor Defeating some important motor protection ?

How big are these motors?  What is the load?  Does the load ocassionally drive the motor?  Conveyor belts running down hill are the extream case of this, some times pumps can act as turbines.  Would these conditions trip a negative sequence relay?

RE: Essential-Service Motor Defeating some important motor protection ?

(OP)
BJC,
The motor rating vary from 500 hp to 1000 hp. These motors drive fans.

RE: Essential-Service Motor Defeating some important motor protection ?

Negative-sequence overcurrent and negative-sequence overvoltage relays can be desirable for ‘smaller’ motors.  One example is a set of submersible pumps that serve water to a research facility.  The cost of removal of one of these motors for inspection was greater than that of the motor itself, and exceeded the installed price of the protection scheme by an order of magnitude.  ANSI C37.96 §2.7  

RE: Essential-Service Motor Defeating some important motor protection ?

Busbar is correct.  To get a motor that size rewound will be a significant cost.  In addition, you will have the labour involved in removing and installing it, and the lost production associated with an OOC unit.  You may want to consider retrofitting your system with a fully integrated solid state motor protection unit?  Many of the modern units have multiple functions including 37, 46, 49, 50, 51, 51G, &86, just to name a few.  Also, many manufacturers have engineering services that will do the engineering, specification, installation, testing, and commissioning for you.

I, personally, have never had much luck with stand alone Negative Sequence Relays, especially the electro-mechanical type.

To answer your original question.  ABB, Basler, & GE have stand alone 46 devices.  However, if you are going to have someone do retrofit work, you may want to investigate a full motor protection unit.  The following are some manufacturers sites.

Cutler-Hammer
https://www.ch.cutler-hammer.com/docs/Fred/apscpgh/htmL/products/mp3000/mp3000.htm

GE
http://www.geindustrial.com/industrialsystems/pm/catalog/indexa.htm

ABB
http://www.abb.com/

Siemens
http://www.e.ptd.siemens.com/webapp/EVWebApp/index_en.jsp

Startco
http://www.startco.ca/products.html

Basler
http://www.basler.com/html/pcsdf-25.htm#MPS100

RE: Essential-Service Motor Defeating some important motor protection ?

What kind of relays do you have in the system?
and is it possible for the system to push air through a fan and put the motor in an unloaded position or in a power  generating mode.  
I have worked on systems with parallel fans and faulty dampers. One fan would cause the other to run backwards and make it difficult to start.
If you had a situation like an FD and ID fan in a boiler the ID fan could suck enough air through and ID fan to cause it to unload and even act as a generator.
 Some relays are smart enough to determine this even though you may know know the feature is active.  It's for conditions where a pump impeller could be unscrewed from a pump shaft by flowing water.
I may be off here but I would like to study this problem more when I have time. Thanks

RE: Essential-Service Motor Defeating some important motor protection ?

I'm a little skeptical about whether a light-load or revserse power situation would actuate a negative-sequence relay.  The relay is intended to detect unbalance currents. It is true that negative sequence stator currents do correspond to stator field rotating in the reverse direction.  However if a motor should go in to reverse power situation, presumably all three phases would undergo a 180 degree phase shift (with respect to the terminal voltage reference).  Mathematically, this does not change the rotation sequence (abc or acb).  In physical terms, it should be apparent that the direction of rotation of stator field will be the same as the direction of rotation of the rotor whether the machine is acting as an inducation motor or an induction generator.  Imbalance and harmonics can add components of the field which rotate in opposite direction, but the fundamental field must travel in the same direction for power transfer to occur.

RE: Essential-Service Motor Defeating some important motor protection ?

yamin
 I can't comment directly on the details of these protection relays. I simply don't know the units. But you are saying you are having lots of trips - how many per motor say per day or week etc??.

If your problem extends across the range then you have a systemic problem. not indivudual motors or units. eg The set up is wrong the units are wrong you may even have an operating proceedure on your plant which has changed or needs review.

to try and help I suggest the following questions be asked -
when did the problem start.
what was changed at this time
what is the problem. (yeh the motor trips but how and which one)
when does the problem occur (always 3am ? only at start up?)

did some of this info up and post it for us it may help.


hi electricpete - I do agree with you about the low risk of reverse generation but I have seen motors "howling along " when the pump were down and they have tripped the incomers when started because the operator forgot to close the dampers before start up - just simply on the reverse flow or flood back. (i have heard of but not seen, shafts sheared by the same process)

Regards to all
Don

RE: Essential-Service Motor Defeating some important motor protection ?

Don - I have heard of but not seen what you describe as well (attempting motor start when the motor was rotating backwards).  It's an interesting subject.  Here are my thoughts about it.

The common scenario would be two fans or pumps feeding a common discharge header.  The one that is not running tends to be spun backwards by the reverse flow (if not check valve, backdraft damper or anti-reverse-rotation ratchet device is present).   Here's my understanding of what happens when we attempt to start it:

The starting current and starting torque can go either direction (above normal or below normal).  The reason is that there are two competing effects when below zero speed (slip is more than 1):
A - Induced rotor current has a higher frequency so the rotor and rotor reactance is higher and tends to reduce inrush current and initial torque.
B - Induced rotor voltage is higher (proportional to relative speed). This tends to increase inrush current and initial torque.

Another way to visualize the torque when below zero speed is to extrapolate the torque-speed curve below zero.  The extrapolation should be relatively smooth.  Depending on the slope of the torque speed curve as it crosses zero speed (can be positive or negative depending on motor), it's easy to see that the starting torque under reverse rotation conditions migt be either greater or less than under normal conditions.

The starting time will always be longer than normal, since the rotor/load has to accelerate further.  Particularly important for a fan which is a high-inertia load to begin with.

RE: Essential-Service Motor Defeating some important motor protection ?

electricpete and don01.
My point in asking yamin what kind of relay he had was to see if some of the senarios discussed above could be happing and no one was aware of it.  Some solid state relays have so many funtions that you may not know which of them are programed on. If he has current input ( and I assume he does) reverse power flow could be sensed.
There are applications of generator "anti-motoring" relays used on motors to limit their contribution ot a fault, but it seems to me they would not be fast enough to do any good.
When yamin said "fans" I was alerted to potential system configurations that be contributing to his problem.  Fan systems are notorious for these kinds of problems.  Even with an airflow diagram you have analyze the system and assume some dampers leak.
Yamin could have a fan system where the air flow trys to put power into the system or the air overloads the fans.  Most fans can overload motors if inlet and outlet dampers are tweeked just right.  
I worked on a fan system that an axial flow fan that ran backwards and triped on time/oc just because it took so long to accelerate.  The long term fix was to repair leaky dampers, the short term fix was dynamic braking by running DC current through two windings.

RE: Essential-Service Motor Defeating some important motor protection ?

BJC - Sorry to misunderstand your point.  I initially assumed that you were concluding that reverse-rotating torque resulted in negative sequence stator currents (which sounded plausible on the surface, but is probably not correct).

Sorry about that.  Next time I'll think twice before assuming the other guy is wrong.



RE: Essential-Service Motor Defeating some important motor protection ?

electricpete
No need to apologize.
I think the guy has an interesting problem. On which has potential for some learning.  If we can get all the facts that is.

RE: Essential-Service Motor Defeating some important motor protection ?

(OP)
Guys,
Sorry for late response, I just got back from vacation.
Sharmen tanks for the links, My motor protection right now is one package(multifunction). The option to remedy the problem (right now with my conclusion) is to change to another brand multifunction relay (will cost a lots) or start disabling the function that initiates false tripping and cover the function by installing stand alone relay.

Don01 to answer your quetions:
1. The problem start since startup, I involved in start up.

2. We change the relay to newer serial # or upgrade the old relay, change the setting that considered too conservative.

3. The problem is the relay initiate false tripping like, ground fault or short circuit or under voltage or single phasing trip. Like I said before we've already reroute the wiring hundred times, do standard test and inspection cannot find anything wrong.

4. The problem occurs randomly, I donot see a pattern related to swithing, weather.


I have about 35 large motors and statistic of false tripping is once a week. All motor starts DOL.

I hope you guys can help me on this.

Thanks
Ilyas

4.

RE: Essential-Service Motor Defeating some important motor protection ?

Yamin,
This has turned into a really interesting thread, with some great responses.  I fully endorse what Busbar has had to say, and would add my two cents worth as follows -

It seems to me that your problem may be related to the installation rather than the setting of the relays, based on the random operations experienced.  One point that may be well worth checking is the grounding of the relays and instrument transformer circuits.
Note that the relays are most likely equipped with grounding terminals that should preferably be connected to a "clean" instrument ground.  CT secondary wiring must be grounded at one point only, multiple grounds can cause relay mal-operation for faults on other circuits (primarily ground fault element trips, one of the factors that you note).
Also, look at cable shielding and grounding practices - could there be noise coming in on the relay circuits?  This would apply to instrument transformer and power supply cabling.  
You say that the relay vendor has visited the site and done tests.  Have they not been able to offer you any tangible support?  If not, then you really do need to think about chaging vendors (and maybe advising us here of their identity).  I spent several years working with one of the major relay manufacturers and we would have been extremely anxious to ensure that our product was being properly applied if such a condition as yours had arisen - I would hope that you would get a supportive response from them to resolve your problem.

RE: Essential-Service Motor Defeating some important motor protection ?

Peterb has some good points and they should all be checked.   If all the fans are doing it then I suspect it is a systemic design problem or:
I still betting money on a system problem independant of the relays or the motors.   The more sophisciated
relays have no load trips that sense when the motor is at no load and trip it off line.  The theory being that it found a broken shaft.  
Fans systems can behave stangely especially if the ductwork has parallel and series connections and or/complicated damper arrangements.  You can overload a squirrel cage blower by fulling opening the inlet damper, if you full close it the fan will go to no load. Axial flow fans have different patterns but can go to overload or no load also by flow control.  A fan that is blowing no air, being forced to move to much air can trip.

RE: Essential-Service Motor Defeating some important motor protection ?

Yamin -
Do the motor trips occur only while starting?  Or after the motor has been running several minutes also?

Does your relay give you any indication of which protective feature caused the trip?

Does your relay capture conditions at the time of the trip (love them SEL's).

RE: Essential-Service Motor Defeating some important motor protection ?

Further to what Electricpete (and Busbar) have mentioned, it would be really helpful to know whether the relays in use have any event/oscillograph recording capability and whether they have been giving any data on the trips.  An amazing amount of detailed information is available from some relays - I fully endorse what Electricpete had to say on SEL's capabilities, based on extensive use of their various products on transmission and distribution systems.

In fact, it if the relays do not have this capability, it would be worthwhile to install a temporary "recording" relay in series to capture event data - trigger this relay recording from a trip output of the in-service relay. This will give a good handle as to whether the problem is in the relay or is a valid response to actual system conditions. I have used this technique with great results on distribution systems to unravel really obscure system operational problems.  

RE: Essential-Service Motor Defeating some important motor protection ?

Very good suggestions on the last two post.  It could be expensive and take a while to build a data collection system for the system.  There are PC based systems that will do it.  If I were going to do something like it again I would start with Action Instruments or something similar.  I would also record or monitor system parameters like damper positions,  starting and stopping of other fans, flow ( paddle switches would work ).
I would suggest for starters he have operations ( of whoever runs things ) log their activities ( all of them).  The cause and soultion might be apparent after some analysis.
There was an "industrial  legend" about a power plant that shut down whenever a certain toilet was flushed.  It went something like it was lowering pressure to a sealwater line, which tripped a feed water pump which tripped a boiler etc.

RE: Essential-Service Motor Defeating some important motor protection ?

Suggestion: Visit
http://www.tde.alstom.com/p-c/en/papers.htm
for a paper:
May 2000
"Distributed Intelligence in Integrated Substation Protection and Control Systems"
Dr. A Apostolov

RE: Essential-Service Motor Defeating some important motor protection ?

(OP)
Guys, tanks for your response,
First thing I do is check all the wiring to meet vendor standard on their instruction book. All grounding point are correct for the relay and instrument transformer.
The common thing to all relay that I can think of is DC power supply and grounding. DC fluctuation 0,5 V from 130 VDC, and grounding resistance less than 1 ohm.

The fault occurs after the motors runs for days or months, and suddenly just trip.

Yes my relay can capture wave form and event data when fault occurs.

Here one of my waveform:
VT input for the relay is open delta.
the target was undervoltage trip. when I see the waveform capture Va is in-phase with Vc with no reduce in magnitude
and the VT is common to another 7 relay and only one that act like that,and this problem is always changing to another relay.

Is anyone ever see a fault record and the one voltage wave shifting 120 degrees to be in-phase to another another voltage.


 

RE: Essential-Service Motor Defeating some important motor protection ?

Never saw anything like that. But if you got an undervoltage trip and anomolous indication for voltage then you need to troubleshoot and understand the voltage input some more (sorry if that was obvious).  

There are lots of possibilities.  One that comes to mind is an intermittent open circuit in your PT circuit.  I saw that once caused by intermittent contact at the fuse ferrules in the PT secondary.  Also some potential transformers have draw-out feature which automatically disconnects primary and secondary circuits when the PT is pulled out... a good spot for an open circuit.

I'm not sure I 100% understood your voltage input circuit (open delta on primary or secondary side of the CT's?.. and what setup on the other side).  In any event it seems REMOTELY possible that for an ungrounded power system with a grounded-wye primary-side PT, a momentary ground on the power system would cause the PTs to sense zero voltage on one phase.

RE: Essential-Service Motor Defeating some important motor protection ?

Troubleshooting for an open ciruit do continuity checks on the primary and secondary circuits (as much of the circuit as possible).  Try banging the equipment a little to see if you can cause an open circuit.   

Is there perhaps two different secondary windings on the same PT?  Maybe that explains why one motor tripped and not the other?

RE: Essential-Service Motor Defeating some important motor protection ?

What kind of DC powere supply do you have??  Is it totally isolate?  By Isolated I mean neither side is grounded (floating). In the situations I know of there would be two wires on the DC system and measuring either of them to ground would result in a 0 (zero)volt reading.  Measuring between the wires gets a reading of 125 v DC.
That  is unless there is a device connected to the system that has an internal ground connection. that device may have a direct connection to ground or through a resistance of some value.  
The device may not be connected to the DC system all the time or may operate intermittantly.  This may or may not be related to the tripping problem.  
Grounds  or partial grounds) in DC  systems are sometimes hard to find.  Ths last one I tracked down was in the electronics of an annunciator system.  The DC system would read -30 and +90 volts to ground.
I still think logging and monitoring ALL events will help.  Make sure you have complet schematics (protection, control, computer inputs, and interlocking controls to other equipment) of the fan control circuits as well as everthing connected to your DC buss.  Correlate any event you can with a trip and investingate the schematics for system involved with that action.  Look for thing that can generate a trip signal.

RE: Essential-Service Motor Defeating some important motor protection ?

A pair of PTs (VTs) can be used in switchgear with high sides connected phase to phase, most often in an open-delta configuration tapped from a MV bus through three (or sometimes four) current-limiting fuses.  To accurately reflect primary phase-to-phase conditions, the secondaries are almost always connected in the same open-delta arrangement.  To prevent electrostatically-induced overvoltage on secondary equipment, the winding pair is corner grounded, (and, mentioned by others here, at one point only) with fuses (often 1-6 amp) only in the two ungrounded secondary conductors.  [ANSI/IEEE C57.13.3 §2.6.1]   The PT arrangement will essentially ignore phase-to-ground voltages (a/k/a ‘neutral shift’) on the serving bus, which is acceptable where there are only 3-wire motor loads.  It seems customary to connect PT secondaires to limit voltage to 150 to ground, and/or 150 volts between conductors.

But to recap a bit, the original posting discussed negative-sequence overcurrent (46) trips as the culprit—but recently undervoltage (27) [or possibly 47/negative-sequence voltage] operations are stated as taking motors offline.  It is typical for these voltage elements be configured with definite-/inverse-time tripping characteristics.  Is it possible that seemingly random nuisance trips are the result of ‘hare-trigger’ settings?

Part of the troubleshooting process should cover well-studied ruleouts if unlikely causes, such as CTs with unmatched kneepoints or auxiliary DC transients, causing relay packages to assert falsely.  [See www.pes-psrc.org. . . thanks, Charlie H.]

Electricpete, you raise an interesting point—how about temporarily loading the PT secondaries to eliminate PT/fuse/connection problems?  Two or three 60-watt lamps at the various relay-package terminals would likely do it.  Don’t most MV PTs have thermal ratings of 500VA or better?

I think readers will be very interested in your resolution to such a frustrating problem.


RE: Essential-Service Motor Defeating some important motor protection ?

(OP)
Guys,
Here one wavecaptured from false fault recently occured.
target single phasing trip but the fault recorder still record Ia, Ib and Ic. But Ia shifted to in phase with Ic.

I think if single phasing trip one of the current should be zero.
We check and try to start the motor running and still running till now.
I've done a lot of thinking, I have one substation with the same cofiguration (I mean CT's, PT's and relay setting, that I recall never trip.
One of the unique of this substation is the relay donot send data to DCS using rs485.

Is it any possibility the relay that send the data Its Processor "exhausted" and want a rest for alittle while ?

RE: Essential-Service Motor Defeating some important motor protection ?

Yamin, please advise some details of your electrical system configuration -
- What is the operating voltage of the motors?
- Is the motor distribution system wye or delta?  3-wire or 4-wire?
- What is the winding configuration of the transformer feeding the motor substation? Wye/delta? Delta/wye?  Delta/Delta?  (also advise vector group)
- What type of neutral grounding is used?  (Both HV & LV systems)
- What type of switchgear feeds the transformer HV?  Are there fuses involved?
- Are the motors wye or delta connected?  Is there any other delta connected load?

The phase current will not necessarily be zero for a case of single phasing, if the single phasing is on the HV side of the supply transformer.  The clue to this problem may very well lie in the recordings - more to follow after you provide the above info, as I can see at least one scenario that may explain your recordings.

RE: Essential-Service Motor Defeating some important motor protection ?

Just thinking out loud some more.

On one occasion your relay saw a loss of one phase of voltage.  On another occasion (or possibly same occasion?), your relay saw a loss of current.

Assuming the above two observations originated from a  single common cause eliminates a lot of the possible causes I mentioned: couldn't be a problem in PT circuit (wouldnt affect current). Likewise couldnt be a problem in CT circuit (wouldn't affect voltage).  

It seems like only two types of causes are left:
#1 - The relay is deranged for some reason (power supply/emi noise problems, dcs communications, beta version of the software etc).
OR
#2 - Your motors are seeing an actual single-phasing condition due to loss of voltage or open circuit at some point in the supply (upstream of the PT location).  Since the problem is reported in many different motors it would likely have to be point upstream/common to all of the motors (near to your incoming power).  It seems relatively unlikely that momentary single-phase power interruptions could occur repeatedly without you getting other indications... but possibly worth some monitoring or discussion with your utility company if you don't turn up anything else with the relay.

RE: Essential-Service Motor Defeating some important motor protection ?

pleas send for me total of products
tunk you very mutch

RE: Essential-Service Motor Defeating some important motor protection ?

(OP)
Peterb
Here's the illustration of my system

I have a transformer 11kV/3,3kV Dyn1. The 3,3kV has NGR 200 A. This XFMR feeds a MV MCC. This MCC feeds motors (7 motors) that starts direct on line.
The bus PT's (that connected open delta, the 'B' phase on secondary grounded)act as common PT to all relays on the MCC.
All the motors are star.3 wire connection.
I have 4 substation typical to what I illustrate above.
 
So if the PT did some thing funny it will affect all the relays, does it ?
And the single phasing trip will read 2 phases only not 3 phases currect since the motor starts DOL ?

I'm still confuse, because the wave from fault recorder is not match any theory that told in school or books ?

RE: Essential-Service Motor Defeating some important motor protection ?

Do all relays connected to the common set of PTs show the same problem in their fault reports?  ...at the same time?  

Does the relay manufacturer have any applications-support people with which you can review the reports?

RE: Essential-Service Motor Defeating some important motor protection ?

Suggestion to yamin:
1. Please, provide info Peter have asked for, since it is needed to arrive to some reasonable solutions.
2. Specifically, the power transformer connections and system grounding are needed.
3. Also, the power transformer upstream connections and grounding schemes.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close