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I
Using the generator
GB
F
The frequency, and therefore the number of motor
revolutions, is maintained constant by the motor's speed
regulation system.
Generally, this regulator is of a mechanical type and
presents a droop from no-load to nominal load which
is less than 5 % (static or droop), while under static
conditions precision is maintained within ±1%.Therefore,
for generators at 50Hz the no-load frequency can be
52–52.5 Hz, while for generators at 60Hz the no-load
frequency can be 62.5-63Hz.
In some motors or for special requirements the speed
regulator is electronic; in these cases, precision under
static
operating conditions attains ±0.25%, and the
frequency is maintained constant in operation from no-
load to load (isochronal operation).
POWER FACTOR - COS ϕ
The power factor is a value which depends on the load's
electrical specifications; it indicates the ratio between
the Active Power (kW) and Apparent Power (kVA). The
apparent power is the total power necessary for the load,
achieved from the sum of the active power supplied
by the motor (after the alternator has transformed the
mechanical power into electrical power), and the Reactive
Power (kVAR) supplied by the alternator. The nominal
value for the power factor is cos ϕ = 0,8; for different
values comprised between 0.8 and 1 it is important during
usage not to exceed the declared active power (kW), so
as to not overload the electricity-generating group motor;
the apparent power (kVA) will diminish proportionally to
the increase of cos ϕ.
For cos ϕ values of less than 0.8 the alternator must
be downgraded, since at equal apparent power the
alternator should supply a greater reactive power. For
reduction coefficients, contact the Technical Service
Department.
START-UP OF ASYNCHRONOUS MOTORS
The start-up of asynchronous motors from an electricity-
generating group can prove critical because of high start-
up currents the asynchronous motor requires (I start-up
= up to 8 times the nominal current In.). The start-up
current must not exceed the alternator's admissible
overload current for brief periods, generally in the order
of 250–300% for 10–15 seconds.
To avoid a group oversize, we recommend following these
precautionary measures:
- in the case of a start-up of several motors, subdivide the
motors into groups and set up their start-up at intervals
of 30–60 seconds.
- when the operating machine coupled to the motor
allows it, see to a start-up with reduced voltage, star
point/triangle start-up or with autotransformer, or use
a soft-start system.
In all cases, when the user circuit requires the start-up
of an asynchronous motor, it is necessary to check that
there are no utilities inserted into the installation, which
in the case of a voltage droop can cause more or less
serious disservices (opening of contact points, temporary
lack of power to control and command systems, etc.).
SINGLE-PHASE LOADS
Power to monophase utilities by means of three-phase
generators requires some operating limitations.
- In single-phase operation, the declared voltage
tolerance can no longer be maintained by the regulator
(compound or electronic regulator), since the system
becomes highly unbalanced. The voltage variation
on the phases not affected by the power can prove
dangerous; we recommend sectioning the other
loads eventually connected.
- The maximum power which can be drawn between
Neutral and Phase (start connection) is generally 1/3
of the nominal three-phase power; some types of
alternators even allow for 40%. Between two Phases
(triangle connection) the maximum power cannot
exceed 2/3 of the declared three-phase power.
- In electricity-generating groups equipped with
monophase sockets, use these sockets for connecting
the loads. In other cases, always use the "R" phase
and Neutral.
ELECTRIC PROTECTIONS
THERMAL-MAGNETIC SWITCH
The electricity-generating group is protected against
short-circuits and against overloads by a thermal-
magnetic switch (Z2) situated upstream from the
installation. Operating currents, both thermic and
magnetic, can be fixed or adjustable in relation to the
switch model.
+ In models with adjustable ope-
rating current do not modify the
settings, since doing so can com-
promise the installation's protection
or the electricity-generating group's
output characteristics. For eventual
variations, contact our Technical
Service Department.
The intervention of the protection feature against
overloads is not instantaneous, but follows a current
overload/time outline; the greater the overload
roughly corresponds to a variation of 5% on the value of
nominal current.
In case of an intervention on the part of the thermal
magnetic protection device, check that the total
absorption does not exceed the electricity-generating
group's nominal current.
M
37.
REV.1-09/05
the less the intervention.
Furthermore, keep in mind
that the nominal operating
current refers to an operating
temperature of 30°C, so
that each variation of 10°C
1
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