Delta MM300 Bedienerhandbuch PDF herunterladen (Seite 114)

CHAPTER 6: SETPOINTS PROTECTION ELEMENTS

MM300 MOTOR MANAGEMENT SYSTEM – INSTRUCTION MANUAL 6–27

• I

represents the equivalent motor heating current in per-unit values on an FLA base.

• I

avg

represents the average RMS current at each motor terminals in per-unit values on

an FLA base.

• I

/ I

represents the negative-sequence to positive-sequence current ratio.

• k represents the value of the

Unbalance K Factor setpoint, used to adjust the degree of

unbalance biasing.

The value for k may be estimated as follows.

Eq. 2

In the above equation, I

represents the locked rotor current in per-unit values on an FLA

base.

If a k value of 0 is entered, the unbalance biasing is defeated and the overload curve will

time out against the average per-unit motor current.

The following figure shows recommended motor derating as a function of voltage

unbalance recommended by NEMA (the National Electrical Manufacturers Association). To

illustrate the MM300 unbalance biasing, assume a typical induction motor with an inrush

of 6 × FLA and a negative-sequence impedance of 0.167. With this impedance, voltage

unbalances of 1, 2, 3, 4, and 5% on the motor terminals will result in current unbalances of

6, 12, 18, 24, and 30%, respectively. Based on these assumptions, the derating resulting

from the MM300 unbalance biasing for different values of k is as illustrated in the GE

Multilin curve below. Note that the curve for k = 8 is almost identical to the NEMA derating

curve.

Figure 22: Motor derating factor due to unbalanced voltage

6.3.1.2 Hot/cold biasing

When the motor is running with a constant load below the overload level, the motor will

eventually reach a steady state temperature, which corresponds to a particular steady-

state thermal capacity used. As some thermal capacity is used, there is less thermal

capacity left in the motor to cover transient overloads than is available when the motor is

cold. Typically, the extent of this effect is calculated by taking the ratio of the motor's rated

hot safe stall time to its rated cold safe stall time. The safe stall time (also known as locked

rotor time) is the time taken with the rotor not turning for the motor to heat to a

temperature beyond which motor damage occurs at an unacceptable rate. The term 'cold'

refers to starting off with the motor at ambient temperature, while 'hot' refers to starting

off with the motor at the temperature reached when running at rated load. The method

the thermal model uses to account for the pre-overload state is thus known as hot/cold

biasing.

estimate)ive(conservat

230

estimate);(typical

175

LRLR

k ==

853729A1.CDR

0.7

0.8

0.9

1.0

012345

Voltage unbalance (%)

NEMA

k=2

k=4

k=6

k=8

k=10

0.7

0.8

0.9

1.0

012345

Voltage unbalance (%)

GE Multilin

Derating factor

1 2 ... 109 110 111 112 113 114 115 116 117 118 119 ... 166 167

Kommentare zu diesen Handbüchern

Keine Kommentare

Delta MM300 Bedienerhandbuch Seite 114

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Elektrowerkzeuge Delta MM300