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Interpretation Red Book IEEE Sdt 141

Interpretation Red Book IEEE Sdt 141

Interpretation Red Book IEEE Sdt 141

(OP)
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?

RE: Interpretation Red Book IEEE Sdt 141

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

RE: Interpretation Red Book IEEE Sdt 141

(OP)
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?

RE: Interpretation Red Book IEEE Sdt 141

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

RE: Interpretation Red Book IEEE Sdt 141

(OP)
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.

RE: Interpretation Red Book IEEE Sdt 141

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

RE: Interpretation Red Book IEEE Sdt 141

(OP)
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

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