The cotton processing season in Uzbekistan means the lines operate 22 hours a day and there is zero tolerance for unplanned downtime. In this case, we look at how Elektromotors engineers from Tashkent completed an urgent rewinding of the stator of a 110 kW DAZO-450M-8 engine in 36 hours and helped a cotton plant in the Bukhara region avoid under-delivery of a large batch of fiber. The story is indicative: often the speed of response of the service is more expensive than the work itself.
Customer: cotton factory at the height of the season
The customer is a cotton gin plant, part of a large agricultural cluster. The enterprise is located between Kagan and Bukhara and processes up to 180 tons of raw cotton per shift. The DAZO-450M-8 engine rotated the main fan of the pneumatic conveying system - without it the entire technological process stops entirely: feeding into the gins is impossible.
The machine worked for the fourth season without major repairs. According to the regulations, maintenance was planned for December, but the breakdown occurred on the night of November 11 - at the peak of the acceptance of raw materials from farmers. The technical director contacted our dispatcher in Tashkent at 02:40, and already at 04:15 our mobile team left on the M-37 highway towards Bukhara.
Urgency of the situation: the cost of every hour of downtime
To understand why the customer agreed to the “emergency 24/7” tariff, you need to look at the economics of downtime during the season. The line cannot wait - raw cotton in riots begins to heat up and lose quality after 36–48 hours. Below is the loss calculation presented to us by the chief engineer of the enterprise:
- stopped acceptance - about 4,200 tons of raw cotton “in line” with suppliers;
- fines under fiber shipment contracts are about 0.8% of the cost of the shipment for each day of delay;
- payment for downtime of 84 work shifts;
- risk of writing off part of the raw materials due to moisture content if the storage period is exceeded.
The amount of potential losses for two days of downtime exceeded the annual cost of scheduled maintenance of the entire engine fleet of the plant. Against this background, any budget for urgent repairs turned out to be justified. We sent a full description of the conditions of our 24-hour emergency service to the client in parallel with the team’s departure.
Diagnostics: what the engine showed
The team arrived at the plant at 09:50 - the journey took about 5.5 hours, taking into account the night mode of the route. Dismantling and preliminary inspection took another 2 hours. On site, right in the workshop, we carried out initial measurements with a 2500 V megger and a thermal imager on the body. The results are in the table.
| Parameter | Norm for DAZO-450 | Measured value |
|---|---|---|
| Winding insulation resistance, MOhm | ≥ 5 | 0.02 |
| Phase resistance, mOhm | 32 ± 2% | 31 / 33 / gap |
| Case temperature at the moment of failure, °C | ≤ 80 | 147 |
| Terminal box condition | Normal | Traces of charring |
| Smell from ventilation | Absent | Pungent, burning |
The picture is transparent: a breakdown of interturn and phase insulation with local charring in the area of the frontal parts, a break in one of the phases. Varnishing cannot save it; partial repairs are irrational. The solution is a complete rewinding of the winding with replacement of the slot insulation. By 13:00 the engine was already loaded onto our transport for transportation to the workshop in Tashkent.
Decision: 36 hours from acceptance to delivery
Time is the main resource. Technologists divided the process into parallel threads and brought in a second shift. Below is the actual timing of the work.
| Time from acceptance | Operation |
|---|---|
| 0 h | Acceptance to the Tashkent workshop, photographic recording, marking of terminals |
| 1–3 hours | Removing the old winding, firing the core in an induction furnace |
| 3–5 hours | Cleaning grooves, grinding teeth, measuring iron resistance |
| 5–6 hours | Preparing a new PETV-2 wire with a diameter of 1.8 mm, cutting Nomex 410 groove insulation |
| 6–16 h | Coil winding, laying, phase-to-phase insulation, double star connection |
| 16–18 h | Electrical tests of the winding, check for turn short circuit |
| 18–22 hours | Vacuum-pressure impregnation with varnish ML-92, two cycles |
| 22–30 hours | Oven drying at 130 °C |
| 30–33 hours | Assembly, installation of NU317 bearings, alignment |
| 33–35 hours | Rotor balancing, tests under load 1.15 of the nominal |
| 35–36 hours | Painting, packaging, shipping back to Bukhara region |
Two teams of 5 people each worked in shifts throughout the entire 36 hours. Additionally, a cold winding technologist and a testing engineer were connected. We have worked out a similar regime - we regularly carry out such emergency orders for cranes, elevators and industrial machines. The service category in our price list is electric motor stator rewinding.
Result: testing and return to service
The engine passed the final tests with a reserve. Control measurements were carried out according to GOST 11828:
- insulation resistance - 880 MOhm at 2500 V (norm ≥ 5);
- test voltage 2 U + 1000 V - maintained for 1 minute without breakdown;
- no-load current - 38 A (passport 41 A);
- vibration at idle - 1.4 mm/s with permissible 4.5;
- heating after an hour of operation under load - 71 °C with permissible 90.
The engine was delivered to the plant the next evening. Installation and connection were completed by the customer according to our scheme in 4 hours. The line started up at 23:10 - on the 38th hour from the moment it stopped. The warranty is issued for 18 months with the condition of quarterly cleaning of ventilation ducts and monitoring of insulation resistance before each change of crews. After 4 months, the client ordered from us a scheduled diagnostics of two more machines on the same line.
Financial result for the client
The most interesting thing is the economics of the project from the customer’s side. We asked the chief engineer to calculate the total losses under two scenarios: classic repair in 7 days and urgent repair in 36 hours.
| Article | Scenario 7 days | Scenario 36 hours |
|---|---|---|
| Cost of work Elektromotors | 1.0× (base) | ≈ 1.7× base |
| Downtime line | 168 hours | 36 hours |
| Contract fines | 5.6% of the lot cost | 1.2% of the lot cost |
| Write-off of raw materials | about 12% of received | 0% |
| Payment for staff downtime | 588 person-shifts | 126 person-shifts |
| The final savings in favor of urgent repairs | — | about 14× the cost of work |
In other words, the overpayment for urgency paid off approximately 14 times only due to saved raw materials and missed fines. This is a typical situation for seasonal production in Uzbekistan - for cotton factories, oil extraction lines, vegetable stores and grain elevators. The logic is simple: the price of the engine and its repair in any scenario is less than the daily revenue of a large line, so saving on service speed is simply irrational.
Additionally, after the case, the company revised its internal regulations: now all critical engines on the main line are checked for insulation resistance before each crew change, and the data is entered into a log. This allows you to catch winding degradation 2–4 weeks before complete failure and plan preventive rewinding in the off-season, and not during the processing peak.
Technological nuances of rewinding on DAZO-450
DAZO series machines are asynchronous motors with a wound rotor and a relatively complex winding layout. During urgent rewinding, we make sure to follow several technological rules that allow us not to lose quality at the expense of speed:
- The core is fired in an induction furnace, and not over an open fire - this eliminates local overheating and a decrease in the magnetic properties of the iron.
- We set the groove insulation to class H (“Nomex 410” 0.25 mm), even if the original winding was F - this is a reserve for heat resistance.
- We solder “star-double star” connections with silver-containing solder PSR-45, we do not use crimp sleeves.
- We perform impregnation in two cycles with vacuuming - this is critical for machines operating in conditions of humidity and dust.
- Before assembly, we check the core for iron resistance of no-load losses - this allows us to identify defects in the package, which otherwise would only appear after a few months.
What is important to remember
Several conclusions from the case that we regularly discuss with clients:
- A season's worth of reserve engines is critical - it pays for itself in one incident.
- Insulation resistance should be measured once a week per season, not once a year.
- A 24-hour service contract with a fixed departure time is cheaper than one-time emergency calls.
- Logistics between Tashkent and the regions takes 4–7 hours - it must be included in the plan.
Do you have seasonal production and there is a risk of an accident? Contact Elektromotors engineers via contact page in advance - we will help you draw up a risk map for your engine fleet, calculate downtime scenarios and connect you to the priority travel program from Tashkent to any region of Uzbekistan.