Over the past year, the question of whether the equipment should be replaced has been raised more often than the question of whether the oil should be changed. Many customers ask on the phone not about model selection but about what flow capacity should actually be prepared for now. The answer to that question usually does not lie in the oil analysis data but in the equipment's own accounts.
The age of the oil and the age of the equipment are two entirely separate accounts
Transformer oil, hydraulic oil and gear oil each have their own recommended replacement interval, while equipment replacement follows a different logic. When an old transformer that has been running for more than ten years is to be overhauled, dismantled and fitted with new accessories, the oil in it may still be two years away from the recommended oil change. When the two come together, a very common situation arises: the indicators of the oil itself are still conforming, but the equipment has to be opened for maintenance, the oil is exposed to air and moisture overnight, and the site does not have the purification capability to bring the oil back to a condition in which it can be put into service.
The difficulty with this kind of situation is that it does not follow a cycle. The manufacturer's maintenance plan, the planned overhaul and the outage maintenance plan may all fall in the same week on several machines, so the processing volume appears concentrated within a few weeks, while the machine itself may be used only once in a year. If the purchasing decision is calculated on the annual average processing volume, the result is often that the machine stands idle for long periods and then is not enough at the moment it is really needed.
Converting the maintenance window into the quantity of oil in hand at the same time
The way to re-estimate the requirement is to draw the maintenance plan up as a table, enter the oil quantity corresponding to each machine, the acceptable processing time and the working area available, and then work out the peak. That peak, and not the annual cumulative processing volume, is the basis for selecting the machine. From the site situations we have been in contact with, what usually decides whether the machine is sufficient is the number of machines taken out of service in the same week, not the total for the year.
| Estimation item | Common situation on site | Effect on the equipment selection |
|---|---|---|
| Oil quantity per machine | The differences are very large | Decides whether the processing time is counted in hours or in days |
| Number of machines in the same maintenance window | Concentrated in a few weeks | Decides how many machines have to run in parallel |
| Available working time | Limited by the outage window | Decides the minimum processing capacity of each machine |
| Degree of contamination of the oil | May contain water and dirt after the tank is opened | Decides the number of filtration stages and whether vacuum degassing is needed |
On-site oil processing capability is usually limited by three things
Once the peak oil quantity has been calculated, it has to be established whether the site can actually carry it out. The three usual limitations are whether the working area can take the machine and the oil storage tank; whether the power supply has enough capacity, given that the total power of a ZYD-100 is 72 + 5 kW on a three-phase 380V, 50Hz supply and the incoming line cannot normally be pulled in temporarily; and where the oil goes, whether it is processed on site and returned to the tank or has to be taken away in batches.
- First establish the oil quantity for each machine; this figure can usually be found in the equipment register and is more accurate than a verbal estimate on site.
- Then divide the length of the outage window by the oil quantity to obtain the processing capacity that each machine has to achieve.
- Then count how many other machines have to be processed in the same window; that is the number of machines to run in parallel.
- The value of a mobile model shows most directly at this stage: the TYG-100 has a flow rate of 6000 L/h, can be put in position and used, and there is no need to transport the oil to a fixed site.
Two common purchasing patterns
One approach is to equip the whole capacity at the peak in one go and use the spare capacity for the routine maintenance the rest of the time. The other is to have the fixed machines cover only the routine duty and supplement it with mobile machines during the maintenance window. The first needs a large initial investment but leaves no one short during the concentrated maintenance period; the second saves at the start but requires the machine to be booked in advance and the power supply and the working area to be solved on site.
Which of the two to use turns on a single question: is the maintenance plan fixed or not. Where the plan is clear, configure to the peak; where it changes frequently, fixed machines plus mobile machines are usually more reliable. Neither route is a standard answer; it depends on the customer's attitude to the risk of the time that the machines are out of service.
The account of an equipment replacement ultimately comes down to the figure of how much oil is in hand at the same time in a given week, not to how many years the machine has been in service.