Efficiency - Danfoss VLT 3000 Series Product Manual

Efficiency

138
Efficiency
To reduce energy consumption it is very im-
portant to optimise the efficiency of a sys-
tem. The efficiency of each single
element in the system should be as high
as possible.
Efficiency of the VLT ® 3000 Series (η
The load on the frequency converter has
little effect on its efficiency. In general the
efficiency at rated motor frequency f
the same whether the motor supplies a
100% rated shaft torque or only 75%.
The variable switching frequency influ-
ences the losses in the VLT
The efficiency will drop a little when the
switching frequency is set to a value higher
than 4.5 kHz.
Efficiency of the motor (η
MOTOR
The efficiency of a motor connected to the
frequency converter is dependent on the
sine shape of the current. In general we can
say that efficiency is just as good as at
mains operation. The motor efficien-cy de-
pends on the make of the motor.
®
MG.30.A7.02 - VLT is a registered Danfoss trademark
Normally the motor efficiency drops when
the load is lower than rated torque, com-
pared to operation on the mains.
In the range 75-100% of rated torque the
efficiency of the motor will be almost con-
) stant both when operated by the frequency
VLT
converter and when running directly on the
mains.
is
M,N
In general the internal switching frequency
does not affect the efficiency of small
motors. Motors from 11 kW and upwards
achieve better efficiency (1-2%). The effi-
® 3000 Series.
ciency is improved, because the sine shape
of the motor current is near perfect at high
switching frequency.
System efficiency (η
) To calculate the system efficiency you can
multiply the efficiency of the units of the
VLT ®
the motor (η
η
SYSTEM
: VLT A: 100% load
®
: System (CT) B: 50% load
: System (VT)
)
SYSTEM
3000 Series (η ) by the efficiency of
VLT
):
MOTOR
= η x η
VLT MOTOR