Recent Dome Rotation Faults at WHT

Follow up of dome rotation faults occurring recently and updating the recommended recovery procedures.

There are two classes of fault: TEM-L Faults and Dome Motor Trips

 

1. TEM-L Faults

1.1 Summary

The oldest manifestation of this fault is that the Dome moves spontaneously while ENG mode is selected in the control room.

More recently, it is more common to find the contacts making a rapid, noisy oscaillation when the Dome panel control key is moved from "OFF" to Remote, or you try to move the dome in local control.

Both of these faults are cleared by resetting the TEM-L unit in the dome.

1.2 Fault Reports

26-Mar-2005 FR 16742 Runaway Dome
25-Sep-2005 FR 16916 Contactors for direction jittering, very noisy
25-May-2006 FR 17264 Dome rotating continuously
29-Mar-2007 FR 17633 Dome rotation breakers oscillating on-off

1.3 Recovery Procedure

These are both caused by a TEM-L fault and are cleared by resetting the TEM-L middle cabinet in the dome.

To prevent the dome moving spontasneously during the daytime, the Dome panel key should be switched to the off position at the end of observing.

 

2. Dome Motor Trips

2.1 Summary

This is a persistent fault, usually involving a trip in the circuit supplying the motor in position 9A, even after this motor has been replaced twice. It was replaced after the motor was burned out by high current (2-Sep-2007). The maximum current in this motor was turned down to avoid another burnout and is now liable to trip more often.

So far, these trips have been observed during tracking in the south, not during slewing. The azimuth positions at which trips have occurred have been accumulating: 141, 156, 201, 231, but always in the south and during tracking, when the current demand is supposed to be low.

2.2 Fault Reports

Most of the following faults were with Motor in position 9A. Other motors have trippped during the time period listed below, but 9 is the most common.

Between Feb 2004 and Dec 2006, almost a 3 year period, there were many dome bogie faults and other major mechanical problems affecting dome rotation failture, but they are not listed here. Curiously, there were very few rotation trips during this time.

After late April 2007 the trips on 9A started becoming a regular occurrance.

17-Oct-2003 FR 16017 Dome motor power trip caused 2hrs of vignetting
29-Feb-2004 FR 16165 Dome motor power 9a had tripped

3 YEAR GAP

05-Dec-2006 FR 17490 dome driver 9 trip fault
22-Dec-2006 FR 17509 dome not rotating
26-Apr-2007 FR 17677 Dome rotation power trip, circuit 8b
13-May-2007 FR 17687 dome stop rotating
20-May-2007 FR 17697 dome stop moving, AZ 141
01-Jun-2007 FR 17711 Dome motor tripped
10-Jun-2007 FR 17724 dome stop during tracking, AZ 201
16-Jun-2007 FR 17737 Dome stopped tracking at AZ 156, cleared by
17-Jun-2007 FR 17738 Dome stopped tracking at AZ 201, vignetting exposure
03-Jul-2007 FR 17748 Dome motor tripped, AZ 246.5
04-Aug-2007 FR 17782 Dome motor trip, AZ 156.5
23-Aug-2007 FR 17800 Dome motor trip, AZ 209.5
31-Aug-2007 FR 17807 Dome would not slew in Clockwise direction, AZ 246
01-Sep-2007 FR 17808 Dome stopped tracking, vignetting transit observation
03-Sep-2007 FR 17809 Motor 9A tripped while tracking at azimuth 201 AGAIN!
14-Sep-2007 FR 17822 Dome stopped during tracking. Motor 9A tripped. AZ 231

2.3 Recovery Procedure

Recently, we have been recovering from this fault by toggling the Dome Power switch in the Interlock Crate in the control room, rather than opening the dome power panel, We still go into the dome in order to check which motor has tripped, according to the LED panel.

So far, nothing has been done to improve warning of Dome AZ not tracking Tel AZ.

Click here for the original document describing Safe Recovery Procedure for dome motor trips, including a photo of the Dome Interlock Crate.