Adjustment And Setting; Specifications - Kohler 6EKOD Operation Manual

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Table Of Contents

Table of Contents

Enlarged version

Frequency Setpoint or Cut-In Point

The point at which the underfrequency unloading begins

to take effect is adjustable, allowing the system to be

tailored

for

each

characteristics of the engine have the largest effect on

the system's performance, the engine's response

should determine the unloading point. The unloading

setpoint is the frequency below which the excitation

control will reduce the voltage so that the engine may

begin to recover.

The cut-in point, or frequency setpoint, should be set

0.5--3.0 Hz lower than the normal steady-state band of

operation. If the engine normally operates within a very

narrow range of speeds close to the nominal, a setpoint

of 0.5 to 1.0 Hz below nominal should be suitable. If the

engine normally operates over a wide range of speeds,

the setpoint may need to be 2.0--3.0 Hz from the

nominal. The underfrequency unloading function can

be eliminated by setting the cut-in point below the

minimum expected operating frequency.

Three-Phase Sensing

Three-phase sensing describes how the excitation

control or voltage regulator determines the condition of

the alternator output voltage. Early types of regulators

sensed the voltage on just one phase of the alternator.

Single-phase sensing is not uncommon today as most

alternators are designed to produce balanced, equal

voltage on all three phases. If the loads applied to the

generator set including no load are equal and balanced,

the output voltage on each phase will be nearly equal.

However, in some applications, individual phases may

have unequal or unbalanced loads. In these cases, the

output voltages will not be equal on each phase. In

general, the phase with the greatest load will have the

lowest voltage while the phase with the least load will

have the highest voltage. This is true regardless of the

type of sensing used in the regulator system.

single-phase sensing excitation controller will keep the

voltage of the sensed phase at the voltage adjustment

value. A three-phase sensing system will average the

three phases and hold the average to the adjustment

setting. The average is the sum of the voltages of three

phases divided by 3.

TP-6772

2/14b

application.

Because

As stated above, three-phase sensing does not

eliminate

the

Three-phase sensing balances the inequality of voltage

between the phases to the desired value. In other

the

words, if a system with unbalanced loads uses a

single-phase control feedback, the voltage on the

sensed phase would be at the setpoint while the other

two phases would vary by their proportional loads. For

example, if the sensed phase had rated load while the

two other phases were only loaded at half the rated

value, those two phases would have higher-than-rated

voltage which may be undesirable. If a three-phase

sensing feedback were utilized, the phase with rated

load would be regulated to a voltage slightly below the

rated voltage while the other two phases would be

slightly above the rated voltage (but lower than in the

previous case). The sum of the three, divided by 3,

would be equal to the regulation setpoint.

In a single-phase system, line-to-line voltage is held

equal to the line-to-line voltage adjust setting. In a

three-phase system, the average of the three line-to-line

voltage is regulated to the voltage adjust setting. In

some cases, it may be desirable to keep one phase at a

particular value. Modify the voltage adjust setting higher

or lower accordingly for any unique requirements for the

particular application.