Voltage Drop in MV System

[kvramesh]

I am wondering what is the voltage drop limits per ANSI/IEEE and NEC for MV branch circuit and feeder.

I got a 23kV pri to 2484V sec transformer, connected to a VFD connected to an induction motor (radial system). My induction motor is 2.3kV rated. I see a voltage drop of 7.15% at the motor bus which makes my end voltage to 2306V which is acceptable for the motor

But, is that much voltage drop allowed per ANSI/IEEE? I know for LV system the limit is 5% (feeder 2% and branch 3%). Does the same apply for MV?

Thanks in advance for your advise

 

[weressl]

I am wondering what is the voltage drop limits per ANSI/IEEE and NEC for MV branch circuit and feeder.

I got a 23kV pri to 2484V sec transformer, connected to a VFD connected to an induction motor (radial system). My induction motor is 2.3kV rated. I see a voltage drop of 7.15% at the motor bus which makes my end voltage to 2306V which is acceptable for the motor

But, is that much voltage drop allowed per ANSI/IEEE? I know for LV system the limit is 5% (feeder 2% and branch 3%). Does the same apply for MV?

Thanks in advance for your advise

23kV is one of the standard voltages defined by ANSI, but 2484v is not. (IEEE-141 would be your reference document.)

Since you have an ASD involved that 'converts' the line to whatever it wants it to, your problem is somewhat different from the run-of-the mill VD problem.

If you are at the nameplate rating of the motor, there should be no problem from the motor's standpoint. At constant voltage and frequency. After changing any of the parameters, new rules apply that you need to verify with the motor manufacturer.

The ASD manufacturer would be the the one to ask. Most ASD's can not supply greater voltage than the input voltage. You also have to ask them how they controls and regulation would be affected by the higher than normal cable resistance AND impedance values. ASD's are usuall VERY finicky about cable sizes and associated lengths, so even though the voltage drop may be aceptable but the cable length isn't. Definetly double check with them about cable size and length.

 

[kvramesh]

weressl,
thanks for your sugegstion. you are correct that with ASD/VFD we keep the voltage and frequency at the desired values. We are okay with the cables lengths and types etc. I'm more concerned with the amount of voltage drop I am seeing which may be violating the NEC or IEEE141 standard. Does these standards apply in my case?

The 2484V is a special case...actually i got a three winding transformer each with 1242V secondary and each winding connteceted to a rectifier unit where the rectifiers are connected in series on their load side to make it 2484V suitable for my motors