Pafi (Electrical)
(OP)
1. In the IEC world, LV Contactors up to 1000Vac are covered under IEC 60947-X-X.
2.IEC 60947-4-1 stipulates the Utilization categories.
For alternating current:
AC-1 Non-inductive or slightly inductive loads, resistance furnaces loads,
AC-2 ..... up AC-8b Hermetic...
Dear friends and experts
After much elaboration, I would like to suggest the following preliminary conclusion based on motor name-plate rating N1/N2=1780/880rpm, kW1/kW2=30/15Hp, I1/I2=29/28A.
1. There is some thing wrong when running N2=880rpm but I2>I1
Suggested possible causes:
a) wrong...
LionelHutz (Electrical)
1. " ....A 30hp motor these days will have an efficiency that peaks around 92% to 94%, not 87%. Also, the efficiency question is in regards to a 880rpm motor and not a 1800rpm motor. The lower speed ..."
My post dated 1st August
Reference to Motor application and...
zlatkodo (Electrical)
1 "Your explanation does not answer the question what causes a high amps at low
speed."
What I wish to stress is when N1>N2, kW1>kW2 and I1>I2. There is something wrong when N1>N2 with I2>I1.
Suggested possible causes:
a) wrong winding termination e.g. wrong terminal...
To KNMurphy (Mechanical)
(OP)
1. One of the reputable VFD drive manufacturer states
a) stationary installation ambient temperature 0...40degC. Max. 50degC if Pn and I2 decreased to 90% ".
b) storage and transportation in the protective package -40...+70 degC "
c) Relative humidity <95%...
To LionelHutz (Electrical)
1. "Do you have proof that the motor at 25% load operates at "very low efficiency"?"
Reference to Motor application and maintenance handbook by Robert W. Smeaton
page 3-47 Fig 33 Typical efficiency curves of 1Hp to 10kHp from 25% to 100% load; for 1800rpm...
To zlatkodo (Electrical)
1. "Another information (if any), might be useful: no-load Amps in low and high speed-connection".
Usually no-load Amps in low and high speed-connection are NOT useful. These data are not needed for engineering design. That is why these data are usually not listed in...
To davidbeach (Electrical)
(OP)
1. In my 50 years of working experience on LV systems, I have NOT noticed any practical significant error irrespective of whether the conductor is placed perfectly in the centre and continue straight for some distance before or beyond the CT.
This can be easily...
FBW (Industrial)
(OP)
1. Your present motor is intended to operate on 1780/880rpm. The kW1/kW2=30/15 is a total mismatch.
Assuming 30Hp is rated for 1780rpm, the motor rated 15Hp would be far too high when running
on 880rpm. It does NOT cause any damages physically but financially as it would...
FBW (Industrial)
(OP)
1. "... i would guess this to be a constant torque motor, given that low speed HP is half of high speed, and little change in current in either speed (28/29)".
Yes, where N1/N2 = kW1/kW2 = around 1/2 is usually classified as a "constant torque motor".
2. " The motor is...
To FBW (Industrial)
(OP)
1. " having studied the circuits for both the high and low speed, it seems to me that i should expect to see a substantial current drop in high speed, as what was once 2 windings in series (1 pole) has essentially become 2 windings in parallel (2 pole). Am i correct in...
To Mr archibaldtuttle
1. Your observations
a) [single-phase] compressor motor always struggle with cold starts],
b) motor melt down when overload failed on a cold start.
2. Assuming the unloader, centrifugal switch or starting current relay are in order; the likely problem is the starting...
sw88 (Mechanical)
What is the Singapore fire code SSxx you are referring to?
Do you have a copy of the SSxx Code and read it?
Info: You can buy the Singapore standard SSxx on-the-spot in Singapore or "read" it, if you are a member of the library.
Some Singaporeans may be be able to chip in...
To krisys (Electrical)(OP)
In the IEC world, for "Low-voltage switchgear and controlgear assemblies" was previously covered by IEC Standard 60439-., now replaced by new IEC 61439-.
The IEC 61439-1 defines the general requirements for all the following product sections in the 61439-. series.
In...
To richerdick32 (Electrical)(OP)
In the IEC world, the general opinion and practices are:
A. For motors
Motor slip rings removable covers, cable-box removable covers and the like; the usual [metal screwed connections or clamping force by the metallic locking mechanisms] are (considered...
CanuckEngineer (Electrical)(OP)
1. Assuming "The pump supplier technician said the motor burnt out on a loss of one phase for an extended period" is correct, then the problem is within your plant, not the utility.
The problem can be resolved by taking following actions:
A. Replace all...
To dithomas (Electrical)
(OP)
1. If your motor is [insulated from any earth except through the insulated PE conductor] which runs through the ZCT, the GFI relay
would NOT function. Under earth-fault condition, [the sum of three-phase currents and the earth-fault current would be equal to...
To mbk2k3 (Electrical)
(OP)
1. " One of the proposed solutions to detect ground fault in the 480V switchgear is to add zero-sequence CTs on each feeder, as this would help identify which feeder the ground fault exists on, and using this zero-sequence CT with the Digitrip 1150 or an external...
To PRincez (Electrical)
(OP)
1. " I am not comfortable with this and want to back the intent up with an IEC or BS standard. "
I suggest you may look up the following documents on this matter:
a) BS 7671 : 2008 Clause 537.2.2.5 , or later editions, and
b) IEC 60364-5-53 :2002 Clause 536.2.1.2...
