TPWRD-00683-2009 1 Abstract—With the increasing use of high-voltage AC cables at transmission levels, phenomena such as current zero-missing start to appear more often in transmission systems. Zero-missing phenomenon can occur when energizing cable lines with shunt reactors. This may considerably delay the opening of the circuit breaker, leaving the system unprotected and vulnerable to failures. Methods to prevent zero-missing phenomenon are still being studied and compared in order to identify effective countermeasures. This paper contributes to these efforts, by presenting several countermeasures that can be applied to reduce the hazards of zero-missing phenomenon. The authors discovered that this phenomenon can be eliminated, merely by using an extra circuit breaker or a pre- insertion resistor. Index Terms—Power Cables, AC Circuit Breaker, Shunt Reactor, Switching Transients, Level-crossing problems I. INTRODUCTION ERO-MISSING phenomenon is defined as an AC current not crossing zero value during several cycles. If a current does not cross zero value it is not possible to open the circuit breaker without risk of damage, except if the circuit breaker is designed to interrupt DC currents or open at a non-zero current value [1][2]. Because of the large capacitive reactive power of HVAC cables, shunt reactors are needed for power compensation. For unloaded cable systems, the shunt reactor current is almost in phase opposition to the current in the cable, reducing the amplitude of the resultant AC component through the circuit breaker. As the current in the shunt reactor has a transient DC component, the resulting current in the circuit breaker may have a DC component larger than its AC component. When Manuscript received September 07, 2009. This work was supported in part by the Danish Transmission System Operator, Energinet.dk. F. F. da Silva is a PhD student at the Institute of Energy Technology, Aalborg University, 9220 Aalborg, Denmark (e-mail:ffs@iet.aau.dk). C. L. Bak is with the Institute of Energy Technology, Aalborg University, 9220 Aalborg, Denmark (e-mail: clb@iet.aau.dk). U. S. Gudmundsdottir is a PhD student at the Institute of Energy Technology, Aalborg University, 9220 Aalborg, Denmark (e-mail: usg@iet.aau.dk). W. Wiechowski is a Senior System Analyst at the Planning Department of Energinet.dk (e-mail: wwi@energinet.dk) M. R. Knardrupgård is with the Planning Department of Energinet.dk (e- mail: mra@energinet.dk) . this happens, the current passing through the circuit breaker does not cross zero until the DC component becomes smaller than the AC component. During its energization the cable is unloaded, and the resistance of the system (cable+shunt reactor(s)) is very small. As a result, the DC component may take several seconds to be damped, period during which the circuit breaker cannot be opened. This paper is an extension of [3], and for a 50 Hz power frequency it describes zero-missing phenomenon and presents countermeasures that can be used to avoid it. The countermeasures are divided into two types: Cases where the shunt reactor is directly connected to the cable and cases where the shunt reactor is connected to the cable via a circuit breaker. II. ZERO-MISSING PHENOMENON AND SWITCHING OVERVOLTAGES A. Basic Circuit: Inductor in Parallel with a Capacitor An easy way of understand zero-missing phenomenon is by analysing an inductor in parallel with a capacitor of equal impedance. In this situation the currents in the capacitor and inductor have equal amplitude and are in phase opposition. The current in the inductor can also have a DC component, whose value depends on the voltage at moment of connection. If the inductor is connected at peak voltage the current at t(0 + ) is zero, if it is connected for zero voltage the current has a peak value at t(0 + ). As the current in the inductor must maintain its continuity, and it was zero at t(0 - ), if the voltage is not at a peak value during connection, a DC component will appear in the inductor current to maintain its continuity. The DC component is equal to minus the value of the AC component at t(0 - ) [4]. If there is no resistance in the system, the DC component is not damped and it will be maintained infinitely. In reality there is always some resistance and the DC component disappears after some time. Fig. 1 shows an inductor in series with a resistor, both of them in parallel with a capacitor. The resistance is 100 times smaller than the inductor reactance, which is equal to the capacitor reactance. Fig. 2 shows a simulation of Fig. 1. The circuit breaker closes when the voltage is crossing zero, and therefore the DC component in the inductor is maximum. The inductive and capacitive AC components cancel out (IL and IC Methods to Minimize Zero-Missing Phenomenon F. Faria da Silva, C. L. Bak, U. S. Gudmundsdottir, W. Wiechowski and M. R. Knardrupgård Z Page 1 of 8 IEEE PES Transactions on Power Delivery 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60