NEUTRAL TERMINAL BOX FOR 6.6KV MOTOR

[GRS1956]

IS IT A MUST TO HAVE A NEUTRAL TB FOR 6.6.KV MOTOR OF 400KW RATED MOTOR MEANT FOR SMALL CAPTIVE POWER PLANT BOILER FEED PUMP APPLICATION.
IN GENERAL NEUTRAL TB GIVES WHAT BENEFITS/FACILITIES

 

[dpc]

I'm not exactly clear on your question, but I will assume you are wondering about the advantages of bringing out all six leads from the motor. The main advantage is that you can apply a true differential relay to the motor, greatly increasing its protection.

It's certainly not a requirement, especially on a motor this small. It is somewhat unusual to apply differential relaying to a 400 kW motor, at least in my experience. It all depends on how long you can live without the motor if it fails.

 

[electricpete]

I agree with dpc I've never heard of separate neutral term box, but seen motors with 3 or 6 leads at main term box.

Another big advantage of having all 6 motor leads available at the main terminal box is an ability to do better motor testing. You can test insulation resistance not just of the whole machine, but each phase to ground. With proper guarding (such as Doble test set), you can also do phase-to-phase tests which provide a more direct indication of end-turn condition (there is very little phase-to-phase capacitance in the slot... only where two phases are adjacent).

 

[jbartos]

Suggestion: There were some postings in this Forum indicating that some Countries require the motor connected in neutral to be connected to the power distribution neutral. Therefore, it depends where the motor will be installed.

 

[swgrmfg]

GRS1956:

In general the neutral TB, if installed, gives you the facility to add Current Transformers for differential protection of larger machines. These usually start at 1000KW. They are more commonly used on generators than motors.