Bogdan Z. Kasztenny

Detection of Incipient Faults in Underground Medium Voltage Cables

This paper presents an operational experience with incipient faults: it has been observed that 10 to 15% of cable faults are preceded by incipient faults. Practically all incipient faults become permanent faults in the period between a few seconds to few weeks. Incipient faults occurring in fast successions create considerable over-voltages and induce faults on other feeders. A method has been presented to detect incipient faults in a secure and reliable way. The method is secure by checking consistency of the load before and after the event, checking if the event is a single phase event, and checking for duration and consistency between the superimposed fault component and the ground current. The presented method has been implemented and tested using recorded field cases and on a digital simulator. Simplified variants of the method can be implemented by using programmability and flexibility of modern microprocessor based relays. Recommendations are given as to the trip vs alarm applications of the incipient cable fault detection functions. In many cases tripping on the first incipient fault is a prudent application.

Fundamentals of adaptive protection of large capacitor banks

This paper derives correct balance equations for short circuit protection of shunt capacitor banks taking into account inherent unbalances in the protected bank. Four methods are derived: voltage differential, compensated neutral voltage unbalance, phase current balance, and neutral current balance. As can be seen from key equations the proper way of balancing the bank (or banks) involves instantaneous values of currents or voltages. Subtracting the residual unbalance as a time-delayed signal (a historical, or a constant value), and responding to the delta changes does not constitute a proper, sensitive and secure operating equation for protective relaying purposes. The methods presented in this paper compensate for both bank and system unbalances. Therefore they are insensitive to major system events such as close-in faults. Presently used relaying techniques might misoperate on such system conditions, as they typically disregard system unbalances and compensate for the bank unbalance assuming no, or minor system unbalances.

Fundamentals of Adaptive Protection of Large Capacitor Banks - Accurate Methods for Canceling Inherent Bank Unbalances

Shunt capacitor banks (SCB) are installed to provide capacitive reactive compensation and power factor correction. This paper derives technically accurate operating equations for capacitor bank short circuit protection that are derived assuming both inherent capacitor bank and system unbalance. The presented relay protection methods allow compensating simultaneously for the bank inherent unbalance and system unbalance increasing both sensitivity and security of protection. The presented methods also facilitate auto-setting and self-tuning applications

Monitoring ageing CCVTs practical solutions with modern relays to avoid catastrophic failures

Ageing coupling capacitor voltage transformers (CCVTs) can pose safety problems and possibly restrain system operations. Catastrophic failure of a CCVT could start a widespread fault in the substation and/or endanger personnel working in a close proximity. The latter becomes a real danger when inspecting a suspicious CCVT or when live line work is being performed. CCVT monitoring becomes more and more important as the installed population of CCVTs ages with sporadic incidents of catastrophic failures alerting both field personnel and dispatching managers regarding safety and liability. Microprocessor-based protection relays facilitate cost-efficient and broad deployment of CCVT monitoring functions across the organization. First, modern relays allow programming a number of indicators that alone, or in combination, are reliable enough to raise alarms and initiate an in-depth engineering analysis. Second, these relays can provide data recording and remote access. This data includes high-resolution data such as oscillography, and long-term trending such as the magnitude profiling. Third, relay-based CCVT monitoring schemes can be retrofitted in the existing installations. In many cases with a simple wiring and setting changes, existing relays could provide a solid CCVT health indication. The combination of reliable alarming via protective relays with remote access yields a cost- efficient, easy to implement, and safe to operate, solution. This paper presents a number of CCVT health indicators that could be programmed on modern relays via logic and simple math operands in order to monitor the CCVTs with a minimum material and labor investment.

Fast and Secure Numerical Breaker Failure Protection

This paper presented two algorithms for enhanced numerical BF protection. The fast reset algorithm for current-based BF detector is based on differentiating between the rotating pattern of a fault current and the decaying pattern of a subsidence current. The algorithm is simple, yet very fast and robust. It uses few factory constants, but they have well defined meanings and can be easily fine tuned in any particular implementation that follows our approach. The algorithm can be further enhanced by recognizing that when the current vector stops rotating and starts decaying due to subsidence, it actually rotates at a significantly lower rate, but in the opposite direction compared with an alternating current. This reversal of the angular speed can be used to strengthen and speed up the algorithm

Application of Modern Relays to Dual-Breaker Line Terminals

This paper discusses several protection and control aspects in relation to dual-breaker line terminals. First, breaker failure and reclosing functions are discussed as applied to dual-breaker configurations. Second, the paper talks about protection security as related to saturation of current transformers (CTs) under fault currents flowing locally through the two breakers. New generation of microprocessor-based line relays support dual CT inputs to monitor both breakers individually, and three voltage points to provide for the main line protection, and synchrocheck across both breakers. The paper points to advantages and disadvantages of integration protection, and provides some guidance regarding dual-breaker line applications