General options – NORD Drivesystems B1000 User Manual

Page 700

www.nord.com

G698

G1000 – Subject to Change Without Notice

General
Options

MOTORS

Thermostat (TW)

Three bimetallic switches are connected in series in
the motor windings, one per motor phase. Upon
reaching the limit temperature, this device automat-
ically opens circuits. The installer is responsible to
wire the thermostat into the motor control circuit.
After the temperature has fallen below the trip limit,
the thermostat switch re-sets automatically. The
auto resetting property must be considered when
designing the safety aspects of the control scheme.

Thermistor (TF)

Three positive temperature coefﬁ cient (PTC) thermis-
tors are connected in series in the motor windings,
one per motor phase. Thermistors require an
external tripping device. Upon reaching the limit
temperature, the thermistors change their resistance
suddenly. In connection with a tripping device, this
property is employed to monitor the motor tempera-
ture. The relay built into the tripping device has a
make-and-break-contact, which is used in the control
wiring. NORD does not provide the external tripping
device with the TF thermistor option. You must
request a thermistor tripping device separately. Many
Inverters and PLCs include a built in PTC thermistor
evaluation input.

TF Ratings

Transition Temperature

150 °C +/- 5°C

Resistance < Transition

20 ... 500 . Ω

Resistance > Transition

> 4k Ω.

Reed Voltage

< 7,5 V

Rated Current

< 1 mA

Motor Ambient Temp.

40°C

TW Ratings

NC (Normally Closed)

auto resetting

Voltage

6 to 500VAC

Current 1.6

Resistance

less than 50 mΩ

Motor Protection

Selecting the appropriate motor protective system
is a key factor in reliable motor operation. There
are two common classes of motor protection;
current based and motor temperature based.

Electrical installation codes require at least two
types of protection in the motors circuit, both of
which are normally current based. First is short-
circuit protection normally accomplished by fuses
or circuit breakers. Second is “motor overload

protection” this is normally a device called a “motor
overload” or a “heater.” Current based protection
is effective in some conditions. NORD can provide
two different types of motor temperature based
protection, a PTC thermistor (TF) or a bi-metallic
thermostat (TW). Temperature based protection is
more effective motor protection in many situations,
see the table below.

¨ = Limited protection

ª = No protection

Fuses

Motor

Overloads

PTC Thermistor

(TF)

Bi-metallic Switch

(TW)

Over current up to 200%

High inertia starting

Frequent motor starts

Stalling

Single phasing

Supply voltage deviations

Supply frequency deviations

Inadequate motor cooling

Bearing Damage

Build