There are two types of synchroscope available in the market. These are moving iron type synchroscope and dynamometer type synchroscope. We shall discuss in this article the construction and working principle of moving iron type synchroscope.
A moving iron type synchroscope consists of a fixed coil. To maintain the uniformity of the magnetic field, we divide it into two halves. Then we connect this coil across two phases of the 3 phase system.
There is spindle at the center of the space between two halves of the fixed coil. The spindle consists of two iron cylinders. These iron cylinders have two vanes on each. The direction of the upper vane is the opposite of the direction of the lower vane on each iron cylinder.
These two iron cylinders are wrapped with two coils. We connect the coil of the first iron cylinder across two phases of the incoming generator in series with a resistance R. Then we connect the coil of another iron cylinder across the same two phases of the incoming generator in series with an inductor L.
We use this resistor and inductor in series with the coils to produce a phase difference of 90° between the currents in these two coils.
The spindle holds the pointer and damping vane on its upper portion.
Working Principal of Moving Iron Type Synchroscope
Suppose there is no difference in the frequency between the existing electrical system and the incoming generator. At this condition, the moving iron type synchroscope behaves as a moving iron type power factor meter. At that time the position of the pointer indicates the phase difference between the voltage of the existing electrical system and the incoming generator.
Suppose the frequency of the incoming generator does not match with the frequency of the existing electrical system. Due to the difference of the frequencies, there is a rotational torque acting on the spindle of the moving iron type synchroscope. As a result, the pointer of the instrument rotates continuously. The speed of this rotation in RPS equals to the difference between the frequency of the existing and incoming system. Obviously, the direction of rotation of the pointer depends on the fact whether the difference of frequency is negative or positive.
The incoming generator may run faster or slower. If it runs faster, it generates an electrical signal with higher frequency. That frequency will be more than the existing system frequency. Suppose in that condition the pointer will rotate in a certain direction depending on the direction of the torque acting on it.
On the other hand, when the generator rotates slower, its frequency will be less than that of the existing system. Obviously, at that condition, the pointer will rotate in the opposite direction.
Method of Synchronizing
A moving iron type synchroscope has 360° scale. The deflection of the pointer from its zero position implies a phase difference between the voltage of the existing incoming system and the generator. So, during synchronizing, when the pointer becomes stationary at its zero position, we can predict that there is no frequency and phase difference between the existing system and the generator. Then we can connect the incoming generator to the system by closing the parallel switch.
Advantages of Moving Iron Type Synchroscope
- The design of this type of synchroscope is robust.
- The cost of this instrument is cheap.
- This instrument is suitable for continuous operation.
- Since there is no electrical connection in the moving system of the instrument, no sleep rings are necessary for the moving iron type synchroscope.