In some applications, it is necessary to regulate the voltage of transformers connected to two independent buses, which means buses can have different generated powers (or transmitted), so these buses operate at little different voltage levels in some periods. In such cases, the AVR may be used regularly, but it is necessary to pay attention to the points described below for the regulation to be successful.

PT Installation

The PT has to be connected next to the transformer that you want to regulate the voltage. In the case of a low generation system, for example, the installation of the PT must be on the side of the transformer connected to the power generation, because it is not possible to regulate the line voltage, which is adjusted by the regulation system itself.

In the case of a transformer with two secondary windings, it is possible to use two PTs, one for each bus, along with the relay logic that changes the used PT for regulation. Because the AVR only has one voltage input, sometimes it may be necessary to change the voltage reference. 

It is also essential to connect the two PTs right at the transformer input, before the circuit breakers, and the two buses' PTs connection be the same, meaning that both need to be measuring VAN, VAB, and so on, this way every time the reference voltage reference changes it will not be necessary to change the parameter CT/PT phase shift.

CT Installation

In the case of a transformer with two secondaries, the primary side of the transformer is the ideal position to place the CT, and the CT ratio multiplied by the transformer ratio at the nominal tap must be parameterized. This way, in any situation, the approximate powers are measured because if the transformer works at a different TAP position from the nominal one, the transformer ratio will not be the same as the one used in the parameterization.

AVR parametrization

In the "CT/PT phase shift" parameter, it is necessary to consider the phase shift between the transformer's primary and secondary, as this value may change depending on the type of connection. 

Another point to consider is the possibility of power flow inversion alarms. In photovoltaic parks, during the day, the system works as a generator and at night as a load. It is the customer's responsibility to judge if it is necessary to disable the blocking by power flow inversion.