transformer secondary protection
- Thread starter wjb
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short answer: YES
Actually Art 450 determines the OCP for the transformer.
Art 240 is for the conductors. (F) simply states that on other than 2 wire single phase and delta-delta 3 wire transformers the secondary conductors are not considered to be protected by the primary OCP.
Actually Art 450 determines the OCP for the transformer.
Art 240 is for the conductors. (F) simply states that on other than 2 wire single phase and delta-delta 3 wire transformers the secondary conductors are not considered to be protected by the primary OCP.
I'm sorry if my question was not clear. I'm aware that 450 covers OCP for transformers. the question is "is secondary conductor protection required for a three phase delta - wye transformer?". 240.4 (F) says secondary conductors of a three phase delta - delta can pe protected by overcurrent protection on the primary side but does not mention delta-wye, therefore I assume delta - wye needs secondary protecton.
charlie
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His answer still stands.augie47 said:
This is the way I look at it.
If the secondary is 1ph 2w or 3ph3w only primary protection is required because the primary OCPD will see in proportion what the secondary current is. I.e. 480-120 is a simple 1:4 and 480d-240d is a somple 1:2
With a 1ph3w and 3ph4w secondary because they most likely are unbalance currents that flow in the neutral the primary OCPD can no longer see the primary L-L-L currents as a simple proportion to L-L-L-N currents flowing in the secondary and can not adaquately protect the secondary conductors.
If the secondary is 1ph 2w or 3ph3w only primary protection is required because the primary OCPD will see in proportion what the secondary current is. I.e. 480-120 is a simple 1:4 and 480d-240d is a somple 1:2
With a 1ph3w and 3ph4w secondary because they most likely are unbalance currents that flow in the neutral the primary OCPD can no longer see the primary L-L-L currents as a simple proportion to L-L-L-N currents flowing in the secondary and can not adaquately protect the secondary conductors.
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