More On Wye Wye Connected Transformers
More On Wye Wye Connected Transformers
(OP)
thread248-481670: Wye-Wye Transformer and grounding
In the United States, in underground mining applications it is legally required that the source secondary transformer have a neutral point, and the neutral must be grounded through a resistor. The resistor value is chosen to limit the maximum phase to ground fault current to 15 amps or less. For a 3 phase 600 volt system, the resistor value will be 23 ohms or more. In all cases, the source transformer’s primary is delta connected. All loads on the transformer secondary are connected phase to phase. Ground fault detection relays are utilized for instantaneous tripping of the branch circuits if a phase to ground fault condition occurs.
After reading the preceding discussion, it appears that a primary wye connection whose neutral point is solidly grounded will permit secondary zero sequence current to flow. Furthermore, it appears that the magnitude of secondary zero sequence current will in essence only be impeded by the resistor.
Agree or disagree?
Thank You, Jim
In the United States, in underground mining applications it is legally required that the source secondary transformer have a neutral point, and the neutral must be grounded through a resistor. The resistor value is chosen to limit the maximum phase to ground fault current to 15 amps or less. For a 3 phase 600 volt system, the resistor value will be 23 ohms or more. In all cases, the source transformer’s primary is delta connected. All loads on the transformer secondary are connected phase to phase. Ground fault detection relays are utilized for instantaneous tripping of the branch circuits if a phase to ground fault condition occurs.
After reading the preceding discussion, it appears that a primary wye connection whose neutral point is solidly grounded will permit secondary zero sequence current to flow. Furthermore, it appears that the magnitude of secondary zero sequence current will in essence only be impeded by the resistor.
Agree or disagree?
Thank You, Jim
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RE: More On Wye Wye Connected Transformers
RE: More On Wye Wye Connected Transformers
".... #1. In all cases, the source transformer’s primary is delta connected. All loads on the transformer secondary are connected phase to phase. Ground fault detection relays are utilized for instantaneous tripping of the branch circuits if a phase to ground fault condition occurs.
#2. After reading the preceding discussion, it appears that a primary wye connection whose neutral point is solidly grounded will permit secondary zero sequence current to flow. Furthermore, it appears that the magnitude of secondary zero sequence current will in essence only be impeded by the resistor..."
1. If the trafo secondary in Y and the Neutral is grounded through NGR, why "Ground fault detection relays are utilized for instantaneous tripping of the branch circuits if a phase to ground fault condition occurs" ? A small time delay say < 1s would be desirable.
2. If the trafo primary is in D, the secondary is Y, with Neutral grounded directly or through NGR; any ground fault on the secondary will be within the secondary circuit only.
2.1. If the trafo primary is in Y with Neutral grounded, the secondary is Y with Neutral grounded directly or through NGR; any ground fault on the secondary will be limited in the secondary circuit only.
Che Kuan Yau (Singapore)
RE: More On Wye Wye Connected Transformers
RE: More On Wye Wye Connected Transformers
RE: More On Wye Wye Connected Transformers