Westinghouse 150-DHP-500 Breaker 2

[Borti]

What is interrupting rating of Westinghouse 150-DHP-500 Breaker?
According to a Westinghouse manual from 1965 the interrupting rating of this breaker is 21 kA @ 13.8 kV and 25 kA at 11.5 kV. The manual does not specify symmetrical or total current rating.
Conrad St. Pierre in his "A Practical Guide to Short Circuit Calculations" lists this breaker as both symmetrical and total rated, and none of these ratings matches the Westinghouse manual ratings. Some other sources match St. Pirre's ratings.

 

[joepower]

My catalogs show that Westinghouse listed the breaker as both 23 and 25 kA symmetrical at various times. The 1979 and 1985 C37.09 standards called for a 28 kA symmetrical rating:

http://www.joepower.com/toolbox/cbrating/cbrating.htm

It's not a simple question:

http://www.joepower.com/toolbox/cbrateconf.htm

 

[cuky2000]

Probably the nameplate of the breaker could have additional information such as MVA rating, max interrupting and max. Momentary current. To attempt to answer some of your questions or at least start getting other colleagues interested in contribute with you here is some of my though

Q1: What is interrupting rating of Westinghouse 150-DHP-500 Breaker?

A1a: Probably this breaker was rated at that time based on total current method described on the C37.5 introduced on the early 1950s. Circuit breaker was given an MVA rating.

o 21 kA @ 13.8 kV =è 20kAx18.8 kV ~ 500 MVA
o 25 kA at 11.5 kV. è 25kAx11.5 kV ~ 500 MVA

2. The manual does not specify symmetrical or total current rating. Conrad St. Pierre in his "A Practical Guide to Short Circuit Calculations" lists this breaker as both symmetrical and total rated, and none of these ratings matches the Westinghouse manual ratings. Some other sources match St. Pirre's ratings.

A2a: Total Rating:
The equivalent to the total rms current (Irms = SQRT(I²_ac + I²_dc) that it could interrupt multiplied by the rated voltage.

A2b: Momentary rating:
Is the mechanical limit of the maximum peak value of current at ½ cycle equivalent to near ~ 1.1xIrms at a given voltage

o Imom @ 11.5 kV = 1.1x25 kA ~ 27.5 kA
o Imom @ 13.8 kV = 1.1x21 kA ~ 23.1 kA
_{NOTE: 23 kA should be less or equal than the maximum rated interrupting current of the breaker.}

A2c: Momentary rating:
Is the mechanical limit of the maximum peak value of current at ½ cycle equivalent to near ~ 1.6xIrms at a given voltage

o Imom @ 11.5 kV = 1.6x25 kA ~ 40 kA
o Imom @ 13.8 kV = 1.6x21 kA ~ 33.6 kA
_{NOTE: 40 kA should be less or equal than the maximum rated momentary current of the breaker.}

A2d: General Comment:
To estimate the fault level a multiplying factor raging from 1 to 1.6 was considered to account for the decrement of the dc component of the fault based on severity of the interruption do to location (far or close to gen. bus), circuit breaker interrupting time (8,5,3 & 2 cycle) and average assumed on the 1950’s as X/R=15.

_{SUGGESTIONS:
For safety and reliability stand point, probably will be a good idea to perform a system assessment to include the following:
o Effect on actual standard changes (presently based on the symmetrical interrupting bases).
o System has significant growth (source & motor load).
o Changes on X/R and comparison with original bkr testing.
o Natural breaker degradation in time
o Actual safety margin.}

 

[Borti]

Thanks guys. Some new light on my problem. If I could confirm the rating from 1965 as symmetrical, my breakers would pass evaluation.