shivam.pandey
Member
- Location
- Chula Vista
- Occupation
- Solar design engineer
Do we need to connect grounding transformer to LV side for each solar transformer?
We have two 2000kVA XFMR connected in loop
Utlity requirement-
Three phase transformers on the load side of Main Disconnecting Means should be equipped
with suitable protective devices to prevent the Loss of Phase condition.
Customers must carefully evaluate the operational characteristics of transformers located on
the load side of Main Disconnecting Means. Many step up / step down transformer
manufacturers use a standard three-legged core design. On a grounded-wye system, the Wye
/ Wye-grounded construction reduces the likelihood of ferroresonance and provides a ground
source. However, under the loss of phase condition (unbalanced voltage) or unbalanced load,
this can create zero sequence voltage (zero sequence flux in the core). In the three-legged
construction, there is no path for this flux to circulate within the core. Thus, the flux jumps
through the tank and air gap. Flux through the transformer tank (enclosure) creates localized
eddy current heating so much as to discolor / overheat the unit and possibly leading to failure.
It is highly recommended to incorporate one of the following transformer options to help
mitigate the conditions:
1. One side of the transformation being Delta connected.
2. A delta tertiary connection associated with the Wye / Wye Configuration.
3. Three individual single-phase transformers connected to form a three-phase bank or
triplex construction.
4. A four- or five-legged core.
5. Shell type core construction.
6. A three-legged transformer with primary protective devices that sense loss of voltage
magnitude and unbalance. When excessive voltage unbalance is detected, all
primary phases need to be disconnected simultaneously.
If this voltage transformation is associated with a DER installation (solar / energy storage /
wind) that utilizes inverters, a Wye / Wye configuration with a Delta connected tertiary
winding may prevent the inverter from sensing a Loss of Phase event on a three-phase
system. The consequence of not detecting the Loss of Phase condition would be a
violation of Standard IEEE 1547. Compliance with IEEE 1547 is required by Ameren
Illinois and Ameren Missouri for all customer with DER interconnections.
We have two 2000kVA XFMR connected in loop
Utlity requirement-
Three phase transformers on the load side of Main Disconnecting Means should be equipped
with suitable protective devices to prevent the Loss of Phase condition.
Customers must carefully evaluate the operational characteristics of transformers located on
the load side of Main Disconnecting Means. Many step up / step down transformer
manufacturers use a standard three-legged core design. On a grounded-wye system, the Wye
/ Wye-grounded construction reduces the likelihood of ferroresonance and provides a ground
source. However, under the loss of phase condition (unbalanced voltage) or unbalanced load,
this can create zero sequence voltage (zero sequence flux in the core). In the three-legged
construction, there is no path for this flux to circulate within the core. Thus, the flux jumps
through the tank and air gap. Flux through the transformer tank (enclosure) creates localized
eddy current heating so much as to discolor / overheat the unit and possibly leading to failure.
It is highly recommended to incorporate one of the following transformer options to help
mitigate the conditions:
1. One side of the transformation being Delta connected.
2. A delta tertiary connection associated with the Wye / Wye Configuration.
3. Three individual single-phase transformers connected to form a three-phase bank or
triplex construction.
4. A four- or five-legged core.
5. Shell type core construction.
6. A three-legged transformer with primary protective devices that sense loss of voltage
magnitude and unbalance. When excessive voltage unbalance is detected, all
primary phases need to be disconnected simultaneously.
If this voltage transformation is associated with a DER installation (solar / energy storage /
wind) that utilizes inverters, a Wye / Wye configuration with a Delta connected tertiary
winding may prevent the inverter from sensing a Loss of Phase event on a three-phase
system. The consequence of not detecting the Loss of Phase condition would be a
violation of Standard IEEE 1547. Compliance with IEEE 1547 is required by Ameren
Illinois and Ameren Missouri for all customer with DER interconnections.