Electrodynamic Power Factor Meter
In electrodynamic power factor meters, we should have knowledge about what is the Power Factor.
The is that a Power Factor is a unit of measurement of various electric drives like induction motors, Synchronous motors Generators, etc. Power Factor is the ratio between the real power and the apparent power. Now the question arises what is real power and apparent power? So, the real power reacts like resistance in an electric drive. It may be called as power consumed in an electric drive or the term “the total load drawn on the electric drive” can be used for the real power. Real power is denoted by Power (P). It is measured in watts (W).
While the apparent power is the product of an electric current and voltage. It is measured in KVAR. It is denoted by S.
Electrodynamic / Electrodynamometer Type Power Factor meters are used to measure the power factor of AC Drives and these meters are of two types according to their phases, which are mentioned below:
- Single Phase Power Factor Meter
- Three-Phase Power Factor Meter
Construction of Single-Phase Power Factor Meter
These single-phase power factor meters are used to measure the power factor of single-phase electric drives and single-phase electric supplies etc. These power factor meters consist of a stationary coil and it is divided into two parts named SC1 and SC2. These coils produce a uniform field that is proportional to the line current. The two moving coils are located in this field which are attached to each other named C1 and C2. These are mounted on a spindle. These moving coils are the voltage coils, C1 consists of series resistance and C2 consists of series inductors. Both moving coils have equal turns on them and these are exactly equal to the same ampere-turns. These two moving coils cannot produce controlling torque in it because the current passes through the ligaments in it, which cannot use control torque.
Working of Single-Phase Power Factor Meter
The current is in phase with the voltage when the load power factor is unity. The current I1 is in phase with the current I and the current I2 lags behind by 90 degrees. The torque acts on coil C1 and sets its plane perpendicular to the magnetic axes of the stationary coils SC1 and SC2. The torque does not act on the moving coil C2. When the power factor is zero, the current lags with voltage by 90 degrees. The current I2 is in phase with the current and the current I1 will be 90 degrees out of phase there is no torque on the moving coil C1 but it acts on C2. It will bring its plane perpendicular to the common magnetic axis of SC1 and SC2.
This instrument must be calibrated at the frequency of the supply on which it is operated for accurate readings. If the frequency of the supply changes its value continuously then this power factor meter will cause serious errors.
Construction of a Three-Phase Power Factor Meter
This instrument is not affected by the variations in frequency. These power factor meters have the same construction as the single-phase power factor meter. The main difference in construction between the single-phase and three-phase power factor is that the moving coils C1 and C2 are at 120 degrees to each other and these moving coils C1 and C2 are connected across the two various phases of the supply. The stationary coils SC1 and SC2 are connected in series with the third phase. The current I1 and I2 are not determined by the phase-splitting circuit.
Working of Three Phase Power Factor Meter
Its working is the same as the single-phase power factor meter works. The main difference is that the current lags with 120 degrees in place of 90 degrees. The current is in phase with the voltage when the load power factor is unity. The current I1 is in phase with the current I and the current I2 lags behind by 120 degrees. The torque acts on coil C1 and sets its plane perpendicular to the magnetic axes of the stationary coils SC1 and SC2. The torque does not act on the moving coil C2. When the power factor is zero, the current lags with voltage by 120 degrees. The current I2 is in phase with the current and the current I1 will be 120 degrees out of phase there is no torque on the moving coil C1 but it acts on C2. It will bring its plane perpendicular to the common magnetic axis of SC1 and SC2.
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