Application Notes
Suggestions for Installing S-02 on Dry / Cast Resin transformers
S-02 is very reliable and has a long service life. When properly handled and installed, it will last throughout the useful life of the transformer and give trouble-free service. Major problems user face in temperature monitoring systems are due to mishandling of S-02, improper S-02 installations and improper wiring. Therefore, take due precautions in handling and installing S-02 and doing correct wiring.
The front portion ( about 2 – 3 cm ) of sensor S-02, contains temperature sensing element and extension joints. This part is very delicate and critical and hence needs utmost care in handling. This portion is well protected by special high temperature sleeves and in normal course nothing should
happen to this. However, tapping, pulling or pushing these wires will surely damage these connections and make S-02 unusable. No heavy object should be put on S-02.
During assembly of transformers, if S-02 is pre-installed then chances of damage to S-02 are very high. It is therefore advisable to install S-02 after the assembly of transformer is complete.
Here are few suggestions for your reference,
1. Providing a tube in the interlayer winding
This is to be done at the time of winding the coils. Take about 8 to10 inches long and 5 to 6 mm ID, mica or epoxy tube. Seal it at one end with epoxy. You need to place this tube along the coil length in inter layer gap at top end of the coil and fix it firmly with fibre glass / cotton tape. This is a good and easy arrangement for housing the S-02. Once the transformer is assembled, S-02 can gently be slide / pushed into this tube. To avoid loose S-02, fill this tube with dry MgO powder and seal the upper end of the tube. This arrangement will give a very long operational life for the S-02.
2. Tying the tube ( after assembly of winding coils )
Take a 8 to10 inches long 5 to 6 mm ID, mica or
epoxy tube, seal its one end with epoxy. You need to tie this tube vertically/length wise on the outer surface of the winding coils by fiber glass or other appropriate tape. Rest of the procedure is as described in suggestion given above.
3 - Drill hole on the top of the winding coils
Drill one hole of about 5 mm diameter and at least 25 mm depth on top side of the coil, at a suitable place, after it is casted. Refer adjacent figure. After transformer assembly, S-02 is to be placed in this hole and secured with some high temperature silicon adhesive. It might be convenient to provide one or two additional holes for installing spare S-02.
This arrangement is more common because it is easy to implement. However, this arrangement calls for extra height of insulation, making coil longer.
4. Putting S-02 in cooling ducts of windings
Some of our customers may find the above suggestions difficult to implement, They may therefore, explore the possibility of inserting S-02 in the cooling duct of low voltage coil. But in that case, care should be taken so that S-02 is not left hanging. The vibration of the sensor should be arrested using some mechanism or using some bonding / adhesive materials of suitable temperature grade.
Connections of S-02 leads to Winding Temperature Scanner ( WTS ). The most appropriate & reliable way of terminating leads of S-02, is to terminate them directly on WTS. This avoids problems arising out of loosening of intermediate terminations and wrong wiring. The only disadvantage of this method is the amount of work involved, in case S-02 is to be replaced for any reason. In some cases, it may not be possible to terminate S-02 directly on WTS. In this case, there will be a necessity to provide some intermediate termination arrangement. Here, care must be taken to select proper terminals, with following considerations.
- terminals are suitable for S-02 leads.
- temperature ratings of these terminals.
IMPORTANT PRECAUTIONS
- Never install S-02 in HV winding coils.
- Avoid S-02 cable running parallel to power / high tension cables, S-02 cables should be grouped with other instrumentation cables.
- Tie S-02 lead wires properly and rigidly so that they are securely in place.
- The excess lead length should be accommodated in the marshalling box rather than in the transformer enclosure.
- Ensure S-02 leads are provided with end ferrules of right size. Never try to solder the free ends of the sensor leads.
- It is advisable to mount S-02 on the LV output side of the transformer. This would avoid the chance of accidental flash-over with HV.
- Always keep the S-02 sensors in their respective packing till they are installed. All spares or extra sensors should be handled in packed condition only.