Panelboard Instruments

Measuring Instruments in the Panelboard

1. Frequency Meter

Ø Measures on how many times an event occur. This frequency meter is usually refrred to as counter. Frequency meter is connected in series with the generators. A problem also with the use of an frequency meter is the need for the meter to be inserted into the circuit and become part of it.

Warning: Mistakenly placing it in parallel with a circuit will blow the fuse, possibly damaging the meter and causing injury. In AC circuits, a current transformer converts the magnetic field around a conductor into a small AC current.

2. kVAR meter

As its name implies, kVAR meter measures or present the amount of reactive power present in a circuit. As we all know, KW and KVAR are confusing.

It seems that usually, one thinks that if KVAR's in a system is equal to zero, then there is no power flowing. (maling mali po). This person fails to understand that real power and apparent power are not the same for a system operating with a no unity power factor. This apparent power is simply circulating power due to the phase shift between the source and the loads. This additional power that appears to be flowing requires the equipment to be rated higher than that for a system operating at unity.

Obviously these circulating currents are really producing no useful work. It is the job of the EE or the power plant operator to correct the load reactance as close as possible to unity to increase efficiency and reduce operational costs. Thus, kVAR meter is very much helpful in the power plant.

3. Kilowatt Meter

Ø The kilowatt-hour meter is designed to reliably, and accurately measure the electrical energy (kWh) used in your home or place of business.

Ø When you look at the face of a kilowatt-hour meter, across the middle you will see a metal horizontal disc that turns when energy is being used. This disc is designed to turn like a motor wheel when energy passes through the meter, and it is calibrated so that one rotation of the disc corresponds to a specific number of kilowatt-hours. This means that depending on the meter make or type, one meter may spin twice as fast as another to register the same kilowatt-hours.

Ø The kilowatt meter and kilovolt-ampere meter measure the power (demand) delivered to the facility being metered averaged over a short duration of time. These facilities are larger users of power than residential or small commercial energy use

4. Synchroscope

Ø A synchroscope indicates when two AC generators are in the correct phase relation forconnecting in parallel and shows whether the incoming generator is running faster or slower than the on-line generator. The synchroscope consists of a two-phase stator. The two stator windings are at right angles to one another, and by means of a phase-splitting network, the current in one phase leads the current of the other phase by 90°, thereby generating a rotating magnetic field.

Ø The stator windings are connected to the incoming generator, and a polarizing coil is connected to the running generator. The rotating element is unrestrained and is free to rotate through 360°. It consists of two iron vanes mounted in opposite directions on a shaft, one at the top and one at the bottom, and magnetized by the polarizing coil.

Ø If the frequencies of the incoming and running generators are different, the synchroscope willrotate at a speed corresponding to the difference. It is designed so that if incoming frequencyis higher than running frequency, it will rotate in the clockwise direction; if incoming frequencyis less than running frequency, it will rotate in the counterclockwise direction. When thesynchroscope indicates 0^o phase difference, the pointer is at the "12 o’clock" position and the two AC generators are in phase.