A
DC haul truck has a retard grid which is used to dissipate heat when
the truck is generating electricity in retard mode. The retard grid
is a series of heavy duty resistors combined with a DC blower that
is connected across part of the grids that uses the voltage drop across
this portion to run the blower.
A loss of this blower could cause the the grid box to catch on fire. The Grid Current and Grid blower current are measured to ensure they are within a correct ratio range and if not RL1 will be energised.
Grid Current is measured on CH1 0 to -1.4VDC = 0 to 1400 amps which comes from existing truck hardware (this signal is Negative - the signal does go positive also but only when the truck is in propel)
The Blower Current is measured on CH2 0 to 5V = 400 amps (0-125A over operational range) which comes from a HCT018 Hall Effect CT.
The limits need to also cover the following:
- System enabled by 24V DC digital signal on input P1
- .After the system is enabled a start-up time occurs usually set to 2 seconds. After the start-up time RL2 will energise and the current measurement logic will start to work (Use the modify wizard on relay 2 and set the on delay).
- .If the grid current is below 250A the alarm sensing function is disabled and relay 1 will remain at it present state.
- .If ('Grid Adc') > ('Blow Adc' x 'BlowFact') for more than 5 seconds relay 1 will latch on (Use the modify wizard on relay 1 and set the on delay).
- .Relay 1 will remain on until reset by input P2.
USC701 Assignments
| CH1: | 'Grid Adc' -1.4 to 0 Vdc = 1400 to 0 |
| CH2: | 'Blow Adc' 0 to 5 Vdc = 0 to 400 |
| P1: | Contact = ENABLE |
| P2: | Contact = RESET |
| RLY1 | Direct acting latch on operation sensing value on M5, On delay Sec: 5, Reset by P2 |
| RLY2: | Direct acting on/off operation sensing value on M6, On delay Sec: 2. |
| M5 | : 'BlowLow', equation output 0 = good 1 = fail |
| M6: | 'P1_State', follows state of P1 input. |
| Con a: | 'MinGrd A' (250) |
| Con b: | 'BlowFact' (8.9) |
| Con i: | 'Zero' (0) |
| Con j: | 'One' (1) |
|
Issue
|
Comment |
|---|---|
 If
unexpected results occur when loading the .usc file press back
and click Help
for instructions. |
|
|
a
|
 (uap1112a.usc
= USC application program.), (uap1112a.pdf
= printable copy of application.) |