When the machine is delivered, the electrical acceptance of many projects ends in two words: normal. The wiring is normal, the trial run is normal, the protection is normal. The trouble is that when something really has to be investigated, none of those three words can be traced back to what was measured, what the reading was and who was present. The value of the electrical acceptance does not lie in the conclusion, but in the handful of lines of data that can still be found and used later.
Why the electrical acceptance has to be recorded in parts
Recording it in parts has three advantages. First, when a fault appears the field of search can be narrowed to one group instead of testing the whole installation again. Second, the responsibility for the groups differs: the grounding belongs to the civil works, the protective devices to the electrician and the interlocks to the equipment supplier, and only separate records stop the groups from covering for each other. Third, the data stays useful for the whole life of the machine: the grounding resistance and the insulation values are still the first line of evidence about the condition of the wiring years later. Writing one sentence in the word normal gives all three of these up.
Group one: grounding
Grounding is the only group that has to be measured and also looked at. A reading inside the limit is not enough if the connection has corroded or the bolt has not been tightened, so the record for this group has to contain at least three things: the measured value of the grounding resistance, the position and the method of the connection, and a confirmation that it has been tightened. The total power of the ZYD-100 is 72 + 5 kW and the supply is three-phase 380V, 50Hz; at that capacity the cross section and the connection quality of the grounding circuit affect the touch voltage directly, and it cannot be handled the way a lighting circuit is.
Group two: insulation and protective devices
The insulation test is about the actual state of the components and the wiring after transport from the factory and after standing idle for a long time, and what it measures is the insulation resistance. The electronic components have to be disconnected before the test, and the record for this group has to state which circuits were disconnected and that they were reconnected afterwards. The protective devices have to be operated one by one: the phase failure and phase sequence protection, the overpressure alarm with shutdown and the motor overload trip. Each of them is recorded with its operating value and the result of the operation, instead of a single tick. For the phase sequence protection it is worth doing a reverse connection test on site to confirm that it really refuses to start.
Group three: interlocks and emergency stop
The interlocks and the emergency stop are the safety related items, and the record for this group has to name what was stopped and not only that it stopped. The cabinet door interlock is verified by confirming that the machine refuses to run with the door open. The infrared level and foam detection is verified by confirming that the circulation stops on a low level or on foam and that the automatic defoaming action starts. The emergency stop is verified by confirming that all the actuators come to rest when it is pressed, and not that only one of the actions stopped. It is not uncommon for these items to be temporarily bypassed or inhibited once the machine is running, so the acceptance record should have a separate line stating whether anything was inhibited at the time.
Group four: the record of the machine running
The last group is the record of the machine running under load: the running current, the difference between no-load and load, the length of the continuous run and the alarm log. The purpose of this group is to set a baseline for the machine. When the same alarm appears a year later, somebody can compare it with the record from that time and see whether it is the same cause, instead of starting to guess again.
| Acceptance group | What is tested | What the record has to hold | The usual weakness in the wording |
|---|---|---|---|
| Grounding | Grounding resistance, condition of the connection | Measured value, position of the connection, confirmation of the tightening | Only "pass" is written, with no measured value |
| Insulation and protection | Insulation resistance, the operation of each protective device | Which circuits were disconnected, operating values, result of the operation | Each protective device is ticked off |
| Interlocks and emergency stop | Whether the refusal and the shutdown work through | What was stopped, whether anything was inhibited | It is not stated whether anything was temporarily bypassed |
| Machine run | Running current, running time, alarms | No-load and load readings, the alarm log | Only one photograph of the trial run is kept |
- Write the measured value and the conclusion separately; the conclusion can be copied, the measured value cannot.
- State on each line who took part and who signed for that group.
- Put any inhibited item on a line of its own with the reason and the time it was restored.
- Keep two copies, one for the equipment file and one in the switch room on site.
The acceptance record is the first set of baseline data the machine has. The more specific it is, the clearer the starting point of every later investigation.
