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1. What if there is a fluctuation in steam load?

The induction generator (IG) never trips due to steam load fluctuations unlike an alternator. The power generator will vary in proportion to the steam flow rate. If steam flow rate falls below a critical value (say <20% of the designed value), the IG will go into the motoring mode.

2. What if there are fluctuations in inlet steam pressure?

Induction generators continue to operate in spite of large fluctuations in inlet pressure unlike an alternator. The power generator will vary in proportion to the pressure at inlet. If it falls below as critical value (say <50% of designed value), the IG will go into motoring mode.

3. Can it be used in parallel with a DG set?

It is possible as long as DG governor is stable and DG power rating is alteast 30% greater than IG.

4. What is the break-up of cost of the ECT?

Turbine Module	:	35%
Gear Box Module	:	25%
Induction Generator	:	20%
Controls and instrumentation	:	10%
Mounting skid and miscellaneous	:	10%

5. How do we control the power factor?

Power factor will be corrected at site depending upon the client’s existing capacitor bank and existing power factor. We will provide banks of 10KVAR and keep adding as necessary at the time of installation, to bring the PF better than 0.85 lag.

6. Is water quality a problem?

For saturated steam applications, no particular care is needed as all the dissolved salts will be in the boiler. If it is good for the boiler, it will be acceptable for the turbine also. Further since we are using hardened stainless steel for the turbine, effects of erosion and corrosion are minimal. In case of super heated steam, silica content needs to be monitored closely (less than 1 ppm).

7. What is the life of the turbine?

15 years, since we are using hardened stainless steel for the turbine rotor.

8. What is the time between overhauls?

It is estimated to be 3 years or more, with an annual inspection.

9. What is the life period of the spares and maintenance?

A. We recommended the following:

Bearing and seals : Annual inspection and change, if necessary
Lube oil change : Every three years

Some fast moving and low cost spares like oil filters, gaskets, relays, etc. will be handy and the same will be advised during installation.
It is advisable to order one set of bearings and seals along with the turbine.

10. What is the life on saturated steam turbines?

A. It is expected to be 15 years since we are using hardened stainless steel for the turbine rotor. However, adequate care is to be taken to ensure that only dry steam enters the turbine and this can be simply accomplished by installing an efficient moisture separator (with thermodynamic trap) and a Y-strainer in the inlet line to the turbine. This is not included in standard scope of supply.

SUPER COOLED VAPOUR:

The steam existing the nozzle will be in a super cooled state and the passage through the turbine takes less than a milli-second. It takes about 1 to 2 secs, for condensation to occur and all the condensation will occur down stream of turbine, hence it is not harmful to the turbine. In addition, since it is a hardened stainless steel blisk, there is no erosion on saturated steam.

11. How does an induction generator work?

Whenever an induction motor is run higher than its synchronous speed by the help of a prime mover it starts generating power instead of absorbing power. All induction machines always operate at a lagging power factor (i.e. the current vector lags the voltage vector and the cosine of the angle of the lag is defined as the power factor). The power factor depends on the slip, which is a function of the loading of the motor. The lag angle will be 90 deg. when the machine runs at zero slip, that is at synchronous speed and this is known as quadrature. At quadrature, it will neither absorb nor generate power. If with the help of a prime mover such as the angle increases beyond 90 degrees and the power factor is negative, which means the machine is generating power. The power factor is adjusted by adding the required KVAR capacitor bank.

Since the excitation of the IG is from the grid, it does not require any governing. Grid acts as the governor. Also it does not call for synchronizing as it automatically locks itself to the grid.

12. What are the safety interlocks provided?

ECT is wired to shut down safely in any of the following undesirable operating conditions:

High lube oil temperature
Low lube oil pressure
Low air pressure (to valve actuator)
Over speed (which is unlikely)
Over voltage
High winding temperature
Earth leakage
Over load

The trip will be annunciated and a hooter will come ‘ON’ and one has to inspect before restarting.

In addition an emergency trip (Mushroom button switch) is also provided.

13. What are the advantages in using high-speed turbines?

ECT is a high-speed turbine. Following are the merits:

For a given enthalpy drop, the turbine diameter is small
Hence for a particular mass flow, the arc of steam admission will be larger
This results in lower losses caused by partial admission
This enhances the adiabatic efficiency of the turbine
This means higher power for the same steam parameters

14. What are the comparisons or differences between alternator and induction generator?

Induction generator has the following advantages:

IG does not require a governor, the associated governing valve actuator
No synchronizing
No load management is required. No load shedding under any steam demand condition
Can accept wide fluctuations in steam flow and inlet pressure
Makes most effective use of process steam flow, maximizes power generation

15. Can the ECT take a mechanical drive?

It is possible to drive, but would require a governor to control the speed of the driven equipment. We will quote on a case-by-case basis.

16. Does a turbine have reverse power relay?

Induction generator does not need a reverse power relay. Since the chances of going into motoring mode are so infrequent and as grid power is essential during starting, reverse power relay is not recommended. If the client insists, the same can be implemented at extra cost. Please be advised that this will have to be bypassed during starting and operational manpower cost will go up. IG does not require any attention and it is a ‘ fit and forget’ system.