1. Field of the Invention
This invention relates to a testing apparatus and more particular to an apparatus which is used for determining the power angle of an AC electrical machine during operation.
2. Description of the Prior Art
The need for monitoring equipment that will accurately provide real time measurements of the characteristics of AC machines is occurring more and more frequently. Because of insufficient monitoring equipment adequate data of machine characteristics during normal and emergency conditions are not provided, thus in some instances contributing to the total collapse of some power systems.
Although some monitoring equipment exists such as for example: The systems disclosed in U.S. Pat. No. 3,052,117 and U.S. Pat. No. 4,091,662 systems such as these do not provide a readily accessible measurement of an essential machine characteristic. This characteristic is known as the power angle. The power angle is the angle between an electric machines' excitation voltage and the system's infinite bus voltage. Mechanically the power angle can be expressed as the instantaneous difference between the angular velocity of the machine's rotor and the machine synchronous rotating magnetic field. In Bulk Power generating systems it is very desirable to monitor the power angle of the electric machines in order to assure the stability of the machines and reduce the risk of power failure.
Standard AC machines which generally operate at a frequency of 60 hertz a .+-. 0.05 hertz should maintain a power angle of less than 90% in order to maintain its stability. If the machine does not maintain its stability this could contribute to a power failure.
In some power systems relays are employed which eliminate the particular machine from the system if the value of the power angle is unacceptable. However, this approach at best makes you aware of the problem when it is already in existence and in some instances this may be too late to prevent power failure.
It is desirable therefore, to provide a means which is capable of continuously monitoring the AC machines in a power system in order that it may be determined at all times whether an undesirable condition is imminent.