are connected to both current and potential

transformers to allow them to measure line

Frequency meters (fig. 5-26) measure the cycles

current and voltage. The kW meter shown in

per second rate of ac. The range of frequency

figure 5-27 is similar to the ones used on gas

meters found on gas turbine ships is between 55

turbine ships. Since each type of generator on gas

hertz (Hz) and 65 hertz. Frequency of the ac

turbine ships is rated differently, the scale will be

used on ships rarely varies below 57 Hz and

different on each class of ship.

seldom exceeds 62 Hz. A frequency meter may

The amount of power produced by a generator

have a transducer that converts the input

is measured in kilowatts. Therefore, when

frequency to an equivalent dc output. The

balancing the electrical load on two or more

transducer is a static device employing two

generators, you should ensure kW is matched.

separately tuned series resonant circuits that feed

Loss of the kW load is the first indication of a

a full-wave bridge rectifier. A change in frequency

failing generator. For example, two generators are

causes a change in the balance of the bridge. This

in parallel and one of the two units experiences

causes a change in the dc output voltage.

a failure. To determine which of the two units is

failing, compare the kW reading. Normally, the

generator with the lowest kW would be the

failing unit. However, you should know there is

Wattage is measured by computing values of

one case where this is not true. During an

current, voltage, and power factor. The kilowatt

overspeed condition, both units will increase in

meters used on ships automatically take these

frequency. But the failing unit will be the one with

values into account when measuring kilowatt

the higher kW load.

(kW) produced by a generator. Kilowatt meters

Before connecting a 3-phase generator to

bus bars already connected to one or more

other generators, you must ensure that certain

conditions prevail. A synchroscope is the device

you will use to find out if the following

conditions have been met:

1. Phase sequence must be the same for

generator and bus bars.

2. Generator and bus-bar voltage must be the

same.

3. Generator and bus-bar frequency must be

the same.

4. Generator frequency must be practically

constant for an appreciable period of time.

5. The generator and bus-bar voltage must be

in phase. They must reach their maximum

voltages at the same time. This is so that when

connected, they will oppose excessive circulation

of current between the two machines.

Figure 5-28 shows a synchroscope. It is

basically a power factor meter connected to

measure the phase relation between the generator

and bus-bar voltages. The moving element is free

to rotate continuously. When the two frequencies

are exactly the same, the moving element holds

a fixed position. This shows the constant phase

relation between the generator and bus-bar

voltages. When the frequency is slightly different,

the phase relation is always changing. In this case,

the moving element of the synchroscope rotates

5-20