ELECTRICAL characteristics

​​​ Standard ELECTRICAL characteristics

​​​B1. Definitions, symbols, unit of measure
The electrical characteristics of motors showed in the following part refer to the symbols and to the definitions reported in the following table.

Definition Explanations U.M. Symb.
Synchronous outputOutput calculated from rated torque and synchronous revolutions per minute​ kW Ps
Rated outputOutput calculated from nominal torque and revolutions kW Pn
Rated torqueTorque at nominal revolutions​​
Nm Mn
Starting torqueTorque at start Nm Ma
Nominal revolutionsRevolutions number at rated torque RPM Nm
Synchronous revolutions Synchronous revolutions number, depending on the nominal frequency and on the motor polarity RPM Ns
Slip Loss of revolutions with reference to the synchronous revolutions s%
Rated current Current absorbed with load equal to the rated torque A In
Starting current Current at motor start A Ia
No-load current Current without load A Io

B2. Connection phases: star/delta​
All motors are manufactured with the possibility either of a star or a delta connection. Unless different requests, motors are supplied with a star connection.
It is however possible, in case of need, to transform the star connection into a delta one following the instructions reported in the use and maintenance handbook or in the wiring diagram in the motor terminal box.
B3. Thermic protection: thermistors at 145°C
Two rows of thermistors, one in the winding of the low speed and one in the high speed one, are always present in the motor. Their implementation prevents motor burning caused by the overheating of the winding. The implemented thermistors are PTC resistors (with Positive Temperature Coefficient ): the value of their resistance ranges from 300 OHM to about 4000 OHM when the temperature of the winding reaches 145°C.
For a correct use of thermistors it is necessary to have a suitable amplificator able to detect its variations of resistance and to inform the control panel, thus opening a contact which can be used as safety contact of the installation. On request, SASSI can supply this type of amplifier.
B4. Thermocontacts at 70°C (to start the auxiliary fan)
Inside the winding, all motors have two thermocontacts to start possible auxiliary fans. Two thermocontacts are connected in parallel. The electrical characteristics of the thermocontacts are the following:

- maximum tension on the contact: 220 V c.a.
- maximum current on the contact: 1 A c.a.

The thermocontact works as a contact normally open which gets closed as soon as motor temperature reaches 70°C. In this way the fan starts working.
B5. Forced ventilation (when scheduled)
It occurs by means of special fans. Standard fans are fed with a single-phase tension of 220V (50/60Hz). Fan can be assembled on all motors; it is therefore possible, without any difficulty, to mount a fan on a machine which was previously not equipped with it.

In the following tables the figures relative to the external permissible moment of inertia (Jest) of the motors for the various types of intermitting services (90-120-180-240 sts/h) refer to the implementation of motors without fan for a service of 90 and 120 sts/h (the latter where scheduled) and with fan for 180 and 240 sts/h.​.
B6. Slip [​S%​]
The slip of two-speed motors is averagely equal to 8% at high speed and to 25% at low speed.
For VF motors please refer to the specific table.

Example: ( motors 4/16 poles - 50 Hz )

High speed synchronous revolutions = 1.500nominal rev. = 1.380
Low speed synchronous revolutions = 375nominal rev. = 280

For each motor the real number of revolutions at full load is printed in the respective plate.

B7. Starting current [Ia]
The starting currents of two-speed motors are averagely equal to:

High speed 3.8 x In2
Low speed 1.5 x In1

In2 = nominal current at high speed;
In1 = nominal current at low speed.​.

For VF motors please refer to the specific table.
B8. Tolerances (CEI 2.3 - Sec.9)
The tolerances allowed as regards the values printed in the motor plates refer to CEI rules 2.3 (Section 9). Here follows​ we sum up the tolerances relative to the most important magnitudes. The values listed in the table represent the increases or decreases ( % ) in comparison to the values printed in the motor plates.​​

Slip +/- 20% compared to the declared slip value
(which can be calculated from nominal rpm)
Starting current high speed + 20%
Starting torque high speed -15% / +25%
Rated efficiency -15% of​ (1 - efficiency)

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