Are RMO25W and RMO10W suited to test OLTC?
No, they are not. However, new devices RMO-T series are designed to test on-load tap changers. These devices will measure resistance change from tap to tap and also, they will measure current change while changing from tap to tap. This allows the operator to take measurements very quickly without discharging, then recharging the transformer for every tap. The winding resistance unit will rebalance after every tap change. In the moment the tap is changed from tap to tap, the device detects a sudden, very short drop of the current value. A properly working tap changer differs from a malfunctioning one, e.g., an interruption during the tap change, and by the magnitude of the ripple value. An interruption will result in much higher ripple value than a properly functioning tap changer.
