rated voltage for feeding 4000 V motor

[cdelp]

Hi all,
I don´t use to work under ANSI standard but IEC so I need your help to understand several ANSI considerations. ANSI Requirements for feeding MV motor is:
- grid rated voltage: 4160 V
- motor rated voltage: 4000 V

Does it mean that 4000 V motors are to be fed at 4160 V at rated conditions so the motor would work under "overvoltage" condition continously?. When motor supplier is going to give the tipical motor curves at 100% and at 80% of the rated voltage, these curves must be provided at 4160/3328 V or 4000/3200 V.

What would be the normal operating values for an ANSI grid (i.e if I supply a 4160/480 V transformer, without changing the taps, the operating voltage at LV bus(480 V) when LV motors and LV loads are working, will drop, so the operating LV value will not be 480 but around 460 aprox. Is this the reason why LV motor rated voltage is 460 V to be use in a 480 V grid?

thank you so much in advance

 

[waross]

Our standard voltages up to 600 V are multiples of 120 Volts.
120 V, 240 V, 480 V and 600 V.
Standard motor rated voltages are multiples of 115 Volts.
115 V, 230 V, 460 V and 575 V.
This is to allow for voltage drops in the feeders and motor circuit conductors.
For many years 230 Volt motors were operated on 208 Volt systems which are quite common for commercial installation. Now, we are seeing 200 Volt rated motors and 208 Volt rated motors for 208 volt systems.
The rated motor voltage is used for specs.
Others with more specific experience with 4160 Volt installations will post in.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

... Does it mean that 4000 V motors are to be fed at 4160 V at rated conditions so the motor would work under "overvoltage" condition continously?. When motor supplier is going to give the tipical motor curves at 100% and at 80% of the rated voltage, these curves must be provided at 4160/3328 V or 4000/3200 V.

The ANSI concept is "Distribution Voltage" vs "Utilization Voltage", with Distribution being what the utility delivers, Utilization being the design voltage of the consuming equipment because, as Bill pointed out, of the expected voltage drop at the line terminals. Design tolerance is typically at least +- 10% tolerance, so a 4000V rated motor is expected to perform "satisfactorily" within a range of 3600-4400V. There will be effects associated with being on the upper or lower ends of the range and it is generally considered better to be on the lower side than the higher side. But if you are at 4160V at the main distribution incoming switchgear, which is where the Utility will take measurements, the chances that you are still at 4160V by the time you get to the terminals of a LOADED MV motor are fairly slim. So I would not consider a 4160V Distribution voltage situation to be the motor working under "overvoltage" conditions.

Motor performance curves would always be per NAMEPLATE voltage, so 4000V in your case (we never use the Y voltage for motors).

A good explanation of the basic concept can be read here in an excerpt from "Energy Matters", a publication of the US Dept. of Energy. They provide a decent chart of what to expect at the different ranges of terminal voltage.

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[cdelp]

Bill, jraef: Thank you so much for your great and clear help