In short. Temporary and bridging power covers the gap when normal supply is unavailable: a failed transformer, a planned shutdown, a delayed DISCOM connection or an expansion that arrives before its permanent supply. The machine is temporary but the engineering is not. A sound project defines why temporary supply is needed, which loads it carries, where it connects safely, how long it will run, and how the site returns to its permanent arrangement.
Emergency, planned and bridging: three different starting points
An emergency rental after a transformer failure starts with urgency and incomplete information. A planned outage for switchboard replacement starts with a date and a load list. A bridging project, such as a new plant waiting for its HT connection, starts with a duration that is uncertain and often extends. Each needs a different level of engineering at the outset, and each can turn into another: an emergency that was expected to last three days becomes a three-month bridge while a replacement transformer is manufactured. The right approach is to establish a safe, minimal power pathway quickly, then raise the engineering review to match the actual duration and risk as soon as the project outgrows its emergency assumptions. See bridging power and planned-outage power.
| Project type | Typical trigger | First priority | Review when |
|---|---|---|---|
| Emergency restoration | Transformer, cable or switchgear failure | Safe connection point and essential loads | Duration exceeds the first estimate |
| Planned outage | Maintenance, upgrade, switchboard replacement | Load list, changeover plan and test before the outage | Scope or date changes |
| Bridging supply | Delayed grid connection, expansion, relocation | Capacity for growth, fuel logistics, service plan | Monthly, against the permanent supply date |
Load priority and capacity
Emergency restoration does not always mean restoring the entire connected load. A factory with a failed 1,500 kVA transformer may need 400 kVA to keep process cooling, compressors and offices running while production pauses, and that difference decides how quickly a set can be mobilised and connected. The facility must state its load hierarchy, since only it knows which loads protect safety, product and revenue. For longer projects, the capacity plan should allow for load to creep back as operations resume.
Fuel per day (litres) = Average load (kW) × Specific consumption (litres per kWh) × Running hours per day
Diesel generator calculator
Fuel use, runtime, tank size and cost
How this is calculated
Real power is kVA × power factor. Fuel use is estimated as L/h ≈ 0.04 × rated kW + 0.22 × load kW, which follows the usual shape of modern diesel gensets: about 0.26 L per kWh near full load, rising towards 0.38 L per kWh at a quarter load because the engine's fixed losses are spread over less output.
If you enter the full-load figure from your engine datasheet, the curve is scaled to match it. Runtime is usable fuel ÷ L/h. Tank size is L/h × hours, plus the reserve margin, divided by the usable fraction.
These are planning estimates, typically within 10 to 15 percent of a healthy engine. Actual use depends on the engine model, its condition, altitude, ambient temperature and how the load varies. For a figure you can rely on, use the manufacturer's fuel curve or a metered test.
Estimates only, worked out in your browser. For a checked selection, send us your load list and site details or call 098852 01608.
Average load is the measured or expected mean load on the set, specific consumption comes from manufacturer data at that load, and running hours are the daily operating period. Worked example (illustrative): a bridging set averaging 350 kW at about 0.27 litres per kWh for 24 hours uses roughly 2,270 litres a day, which means a delivery every day or two from a typical rental fuel tank. Fuel planning is therefore a logistics task from day one. See rental capacity and runtime planning.
Connecting safely
Understanding which element failed tells you where temporary power can connect. If a transformer has failed but the LT switchboard is healthy, the set can usually connect at the incomer through a suitable changeover arrangement. If the switchboard has failed, temporary distribution may have to feed loads directly. Before energisation, the connection point must be isolated from the DISCOM supply so the generator cannot back-feed the network, cables must be sized for the current and run length, the earthing arrangement must give a defined fault return path, and protection must suit the generator’s fault level, which is much lower than the grid’s. Phase rotation must be checked before motors are started. Rental cables and rental ATS describe the equipment used.
Operating and handing back
A temporary set running for weeks needs the same attention as a permanent one: service at its intervals, fuel quality checks, daily log readings and a clear statement of who is responsible for operation and attendance. The handback plan matters as much as the mobilisation. Returning to permanent supply usually means a planned changeover with a short interruption, or a closed-transition transfer if the equipment and DISCOM permit it. The record should note the date, the checks performed on the permanent supply before load was returned, and the condition in which the temporary equipment left the site.
What a credible project record shows
A temporary power record should state why alternative supply was required, the loads supported, the connection arrangement, the tests performed before energisation, the operating period and the handback. A letter of award records intended scope; it does not show delivery or performance, so it cannot stand alone as a case study. Claims about response time or uninterrupted operation need dated records. No approved temporary or bridging case is presented here at present. Other categories are under mining power projects, and general rental options under rental and temporary power.
Common mistakes
- Treating a long bridging project with the same informal arrangements as a weekend emergency. Service, fuel and protection gaps accumulate until the temporary set fails.
- Connecting without isolating the DISCOM incomer. The generator can back-feed the network and endanger line staff, or be damaged when supply returns.
- Restoring every load because the generator is there. The set overloads and the essential loads lose supply along with the rest.
- Planning mobilisation but not handback. The return to permanent supply becomes an unplanned outage of its own.
What to send us
Send the reason temporary power is needed, the required start date and expected duration, the essential load list, a photograph of the intended connection point and switchboard, the distance from generator location to that point, and site access details. For emergencies, the location, load and contact are enough to start. Send a generator rental enquiry.
Questions engineers ask
How quickly can temporary power be connected after a failure?
It depends on generator availability, distance to site, access and how ready the connection point is. A site that has identified its connection point and essential loads in advance can be restored far faster than one that starts planning during the outage.
Do we need to supply the whole plant from the rental generator?
No. Many sites restore only essential loads, which reduces generator size, cable work and fuel. Agree the load hierarchy with operations before the set arrives.
Who is responsible for fuel and maintenance during a rental?
That depends on the rental agreement and must be written into it. Long projects should define service intervals, fuel supply, attendance and response times before mobilisation.
Can a rental generator be paralleled with the grid for a seamless handback?
Only with suitable synchronising equipment, protection and DISCOM approval. Without them, the handback is an open-transition changeover with a short planned interruption.
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Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.