Interpretation Red Book IEEE Sdt 141 1

[roland64]

I need help for the selection from a circuit breaker to 4.16 KV.

For the momentary duty, I calculated the first-cycle network, using a estimated first-cycle reactance of 0.17 pu for motors at 4.16KV, 350HP; a estimated first cycle reactance of 20 pu for motors to 480V, 75 HP and 60 HP.

For the interrupting duty I calculated the interrupting network, using a estimated interrupting reactance of (0.17 X 1.5) pu for motors at 4.16KV, 350 HP; a estimated interrupting reactance of 0.50 pu for motors at 480V, 75HP and 60HP. Standard interpretation Is correct?

 

[alehman]

It's hard to say if your impedance values are reasonable, especially since you didn't specify a base. Your 480V values look questionable with 20 pu for momentary and 0.5 pu interrupting.

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[roland64]

Hi alehman.

The base is motor rating.

For 20 pu in momentary, Table 4-2, column "first cycle network", line "all others, 50 HP and above" 1.2Xd" or estimated the first cycle network X=0.20 pu based on motor rating.

For 50 pu in interrupting, Table 4-2 column "interrupting network", line "all others, 50HP and above" 3.0X" or estimate the interrupting network x=0.50 pu based on motor rating


All motors, the nameplate reactances are missing.

Is correct?

 

[alehman]

I'm confused. By 20 pu and 50 pu, do you mean 0.2 per unit and 0.5 per unit, as per table 4-2 footnotes?

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[roland64]

Hi Alehman

Is correct, 0.20 pu and 0.50 pu according to Table 4-2 foor notes, IEEE std 141-1993.

Pardon went an error when writing the reactance.

 

[alehman]

The purpose of table 4-2 is to avoid the need to differentiate between low voltage and medium voltage motors. For the first-cycle network, it recommends X=0.2 pu for motors 50hp and larger and X=0.28 pu for smaller motors. For the interrupting network it recommends X=0.5 pu for motors 50hp and larger, and neglect smaller motors.

Does that answer your question?

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[roland64]

Hi alehman

For medium voltage motor (350 HP), the nameplate are missing, thens estimated reactance for first cycle is 0.17 pu (at 150 KVA base, 1 KVA = 1 HP), the estimated reactance for interrupting network (0.17 X 1.5)?

Applying Table 4A1, Line "Individual large inductions motors, usually above 600 V": Xd"=0.17 pu of machine KVA ratings