The bonding jumper and grounding electrode connection are two separate requirements. The bonding jumper from the separately derived neutral to the equipment enclosure can occur at either the transformer or the first over current device on the transformer secondary. For this type of installation...
The 300 series has an in-phase monitor that can be enabled or disabled. The ASCO ATS transfers in 150 ms with no neutral position so they come standard with an in-phase monitor to prevent nuisance tripping. The in-phase monitor needs to see two phaser crossing to establish the transition speed...
Does anyone know if there is a manufacturer in the US for the pad mounted ground detection equipment specified in the attached drawing. I could give this to a switchboard manufacturer but was hoping this was a standard product for somebody. Thank you in advance.
Figure 'A, shows the zero sequence CT located above the stress cone and the shield connection routed back through the CT which will result in the current flowing out to the fault to be cancelled by the same current flowing back on the shield. Typically the zero sequence CT is 600 volt rated and...
As mentioned CTs used for zero sequence detection schemes typically have a much lower ratio than the of the CTs used for the phase over current. As such the secondary current in the zero sequence CT is much higher and the CT core requires more iron to prevent saturation. They are significantly...
You also need to be careful in choosing the ratio of the core balance CT to avoid saturation issues if the system is solidly grounded. I looked into a coordination issue recently similar to your situation but the root issue was the saturation of the core balance CT.
You may want to use something like the product attached. I have been using it for over 15 years on systems upto 21KV. http://files.engineering.com/getfile.aspx?folder=d828fafc-10a3-4eca-9764-fa85a8e2d290&file=cablebus.pdf
If you tested the cable for 10 min. at 20.7KVDC you should be fine and I would not think you would need to do more. The DC test voltage for 5KV, 100% rated cable is 25 KV so your 20.7 KV test voltage is a bit conservitive but fine. The test voltage has only to do with the insulation, not the...
On the sample you removed, did you inspect the semi-conductor layer over the XLPE insulation? If the shield is OK and the semi-conductor is smooth,no waves, it will be OK. The main reason for the min radius is to prevent the semi-conductor layer from seperating from the insulation. Air voids...
With only about 35 KVA of connected load, the 75 KVA transformer should have been OK. Our standard specification is for 115 deg C rise transformers for upto 25% non-linear loads and K13 rated past that. I have used this specification in telecommunication facilities, which have mostly inverter...
What is the input voltage to these environmental chambers?
120v, 208v or 120/208v? These can all be single phase.
What was the temperature rise rating of the transformer?
Can you take a photo of the transformer nameplate?
Same Okonite article:
"It is, however, the specter of mechanical damage, or substandard splicing and terminating that could cause the engineers responsible for continuity of service to desire a field applied proof test to establish the cable’s serviceability. The time-honored methods of proof...
DC overpotential testing is the test most typically performed on new cable after installation. If performed properly; regulated power source, proper corona suppression devices, proper test voltage etc., the test is not destructive for new cable. Improper test procedures can damage good cable...
I would look more for the lower temp rise rating than if it has copper or aluminum windings. 150 degC rise transformers have much higher load losses at the same load as does a 115 degC rise unit. The 115 degC rise unit has lower load losses, makes less noise and should last longer. Be sure to...
ScottyUK,
No question PD is a valuable test for determining viability of insulation systems. I was trying a bit of sarcasm in that if the PD tests had been performed regularly, there would have been an excellent base for life assessment. I have a difficult time understanding 10 years without...
Space, budget and operational considerations are all important. All three options are going to be workable and all have pro's and con's. Choose the one that fits best with the conditions you are faced with. Option #2 seems as if it would accomplish the most for the least ammount of space and...
Partial discharge test results are most useful for comparing results on the same equipment over a period of time.
The useful life of the switchgear depends mostly on maintenance, environment, loading and number of faults it may have cleared. Just the basic cleaning,lubricating and exersise on...
Why 5 #250 kcmil? First; that will be a tough pull even in EMT. Second; if #250 kcmil is the phase conductor size, then your overcurrent protection is probably 300 amps or less. Third; the equipment ground conductor needed for a circuit with a 300 amp overcurrent device is #4 (NEC Table...
