Network Voltage vs. Device Voltage 2

[gcaudill]

I am currently designing an electrical distribution system for a plant to be built outside of the U.S.A.. The nominal network voltage is to be 380V/3/50. The motors and other devices being specified for the plant are 380/400/415V rated (basically IEC stuff). My question is this, would it be better to design the network voltage at 400V to allow for voltage drop that occurs between the main switchgear and the actual loads? For example, in the U.S.A. it is common to have a 480V network, but NEMA motors are rated 230/460V. If you have experience in this particular decision, I would love to hear from you.

 

[candu6]

Motors in Canada are rated 575V and our plant bus voltage is 600V.

 

[RRaghunath]

The transformer open circuit voltages are always rated about 5% higher than the system voltages to take care of transformer regulation (when loaded). For example 415V for 400V system, 433V for 415V system.

Hope this is helpful.

 

[Kiribanda]

Hi gcaudill,

As per IEC standard system voltages, 380 V is no longer a standard nominal system voltage after 2003. Instead it will be 400 V (+ 6%, -10%) and the equipment are designed accordingly.

Based on above, if you are designing a new distribution network per IEC standard voltages, I agree with your opinion that the network nominal system voltage should be 400 V and not 380 V.

Then how about the utilization voltages?

As per above, supply voltage can drop down to -10% of nominal. IEC 60364 and IEE wiring regulations (BS 7671) allows maximum of 4% drop within the consumer installation (NEC allows a total of 5%). That means the utilization voltage can drop down to 14% from nominal.

Therefore the motor rated (name plate) voltage should be 380 V (+/- 10%).

We should also keep in mind that

1)ANSI transformer primary and secondary voltages are always in line with ANSI standard nominal system voltages. (ANSI C84.1).

2)In IEC transformers, only the primary voltage is in line with a IEC standard nominal system voltage. (We can order with any secondary voltage which is normally 5% higher than standard nominal)

Hope this is helpful!

Kiribanda

 

[gcaudill]

Thanks rraghunath and kiribanda. Most helpful.