Controlling Resistive Loads; Tripping Behavior; Restrictions For Power Calculation Of Resistive Loads - ABB UMC100.3 Manual

U M C 1 0 0 . 3 U N I V E R S A L M O T O R C O N T R O L L E R T E C H N I C A L D E S C R I P T I O N
94

Controlling Resistive Loads

Consider the following points to monitor and control resistive loads e.g. heat tracings. No real control function is described here
but an operation mode that can be used together with other control functions. To activate this mode set parameter "Resistive
Load" to "YES".
Usage examples
• Heat Tracing: To monitor and switch on/off a three phase heat tracing use the control function DOL
• Load Feeder: To just monitor the current or active power in the three phases use the tranparent control function. For single phase
loads set also the parameter "Number of Phases".

Tripping behavior

• Set parameter "Nominal current" always to the highest current in the three phases. Otherwise the thermal overload protection
might create a trip. Set the parameter "Trip Class" to "Class 40".
• The implemented thermal model follows the figure in chapter "A3 Technical data". UMC100.3 is designed as a protection device
for 3-phase AC induction motors. It is not approved for thermal cable and short circuit protection.
• The cooling function is adjusted to motors.
• In the mode "resistive loads" always the highest current of the 3 phases is input of the thermal model. One common thermal
model for the 3 phases is implemented, which is fed with the highest present current of L1, L2 or L3.
• Then protection functions high / low current trip and warning always use the highest current of the 3 phases.

Restrictions for power calculation of resistive loads

The Phase angle j must always be >= 0°; no capacitive load allowed. Otherwise the results of power calculation are not specified.
Currents must be in Sine wave form. Other wave forms caused by e.g. switching loads can lead to wrong calculations of current,
voltage and power.
Symmetrical network / voltages, so that calculation from 3-phase line to line back to single phase voltages (division by 3rd root) is
possible. Imbalance increase the deviation in calculation of voltage and power.
Active power is calculated as follows:
P = (I +I +I ) * (U
w L1 L2 L3 L1L2
• In the UMC100.3 the power factor is calculated as follows:
PF = COS((abs I U
L1 L1
Remark
If the cosj in each phase is identical, this cosj match the power factor ( active power / apparent power)
Helpful suggestions:
• Set parameter "check phase sequence" = off
• Set parameter "phase loss protection" = off; --> current imbalance protection is also disabled.
Current imbalance calculation is always available: Iimb = 100*(1- Imin/Imax).
Remarks
• No ATEX certificate for this application.
)/3 * PF / √3
+ U + U
L2L3 L3L1
+abs I U +abs I U
L2 L2 L3 L3
) / 3)