Two Wiring Methods for Differential Experiment of Microcomputer Relay Protection Tester
Usually, current transformers are of the subtractive polarity, meaning that the primary and secondary windings of the current transformer have the same polarity at corresponding terminals. During equipment installation, the positive polarity terminals of the current transformers on both sides of the transformer are generally installed close to their respective busbars. At this time, the differential protection can have the following two wiring methods.
Wiring Method One
Method One: "Lead-out from head" method. The secondary winding of the current transformer in delta connection is connected as a-head to b-tail, b-head to c-tail, c-head to a-tail, and the head is used as the lead-out wire; the secondary winding of the current transformer in Y connection adopts the wiring method of connecting tails and leading out from heads. The wiring diagram is shown in Figure 2(a), and the vector relationship is shown in Figure 2(b). Since the transformer connection group is Y, d11, its delta-side current IA""B"" leads the Y-side current by 30 degrees. With the phase compensation wiring, the secondary current Ia""b"" of the delta-side current transformer lags the secondary current Iab of the Y-side current transformer by 30 degrees, which exactly compensates for this phase difference. The differential current wiring creates an additional 180-degree phase difference between Ia""b"" and Iab. Therefore, as can be seen from Figure 2(c), after adopting the differential current wiring and phase compensation wiring, Ia""b"" lags Iab by a total of 210 degrees. In this way, the phase of the currents on both sides of the differential protection fully meets the requirements.
Wiring Method Two
Method Two: "Lead-out from tail" method. The secondary winding of the current transformer in delta connection is connected as a-head to c-tail, c-head to b-tail, b-head to a-tail, and the tail is used as the lead-out wire; the secondary winding of the current transformer in Y connection adopts the wiring method of connecting heads and leading out from tails. The wiring diagram is shown in Figure 3(a), the vector relationship is shown in Figure 3(b), and the phase relationship between the primary and secondary currents of the current transformers on both sides of the transformer is shown in Figure 3(c).
