This application claims priority to European Patent Application Serial No. 12382234.8, which was filed Jun. 7, 2012. This priority application is hereby incorporated by reference in its entirety into the present application, to the extent that it is not inconsistent with the present application.
Generators may be used to supply an uninterrupted supply of power to an AC electrical power grid for many applications. In order to connect a generator to an electrical power grid to supply AC power, the generator must be synchronized to the electrical power grid in order to avoid damage to the generator or other connected rotating machinery. Generally, the generator is synchronized and may be attached to the electrical power grid when the output voltage or current of the generator is at nearly the precise point on its sinusoidal waveform as that of the voltage or current of the electrical power grid. When the two waveforms are substantially synchronous, or in phase, with each other, a circuit breaker connecting the generator to the electrical power grid may be closed. If the circuit breaker is closed before the generator and electrical power grid are in voltage phase alignment, severe damage to the generator, other connected rotating machinery, such as a prime mover, or the circuit breaker may occur.
Typically, a synchronizing relay may be used during a generator start-up to determine when it is permissible to close the circuit breaker relay thereby connecting the generator to the electrical power grid. These devices are generally designed only to synchronize an isolated generator to an electrical power grid by comparing the waveforms on either side of the circuit breaker. As such, these synchronizing relays may not be able to detect system faults including over-current, over-voltage, reverse power flow, over-frequency, and under-frequency conditions that may occur before the closing of the circuit breaker, creating an asynchronous condition resulting in the aforementioned damage to the generator.
To counter system faults, many protections schemes have been introduced to detect and isolate system faults utilizing protective relays. Typically, generators may be equipped with a host of protective relays to isolate the generator from the electrical power grid in certain system conditions. For example, a generator may include under/over voltage and under/over frequency relays capable of detecting potential asynchronous conditions occurring while the generator is temporarily isolated or islanded.
Further, the measurement and monitoring of the generator and electrical power grid characteristics such as voltage, current, frequency, and the like, as mentioned above, may be important to the proper synchronization of the generator to the electrical power grid. Typically, a multimeter may be used to determine, for example, voltage or current of the generator and/or the electrical power grid. However, the requirement of separate equipment to provide each of the measuring and monitoring of the generator and electrical power grid, the synchronization of the generator to the electrical power grid, and the protective relays to ensure system faults are detected and isolated to prevent damage to the generator may typically result in increased capital and operating costs, including installation and maintenance costs, and increased space requirements.
What is needed, then, is a compact and efficient device capable of providing for the monitoring and metering of the generator and electrical power grid, synchronization of the generator to the electrical power grid, and protection of the generator.