- Email: [email protected]
Preliminary power tests of a superconducting alternator
First power tests have been performed on a 500 kW hypersynchronous cryoalternator. To avoid limitation induced by our driving motor, the tests were made at halfspeed up to an active power o f 150 kW, which corresponds to the 2/3 o f the nominal power o f the machine. These power tests are among the first ones made on cryomachines o f this size.
Preliminary power tests of a superconducting alternator Y. B r u n e t , J. M a z u e r a n d M . R e n a r d
A cryoalternator project was initiated at the CNRS CRTBT four years ago. Up to now, only cryogenic and small power tests 1 have been performed on a 500 kW prototype which is built in the laboratory. EDF support made it possible to perform half full power tests on the machine
No anomalous effect appeared when the stator was loaded; during the tests, the load was changed in steps of "~ 15 kW and no perturbation was seen on the superconductor. Although the gliding between the screen and the dipole gives a complicated vectorial diagram of the machine, 3 a good approximation is given for the voltage drop when using a simple Behn Eshenburg theory with a synchronous reactance calculated with the open and short circuit tests (Xd -- 0.4 pu).
Our machine has been specially designed to reduce transient mechanical and heat loads. A thick screen is mechanically driven by a driving motor; when the inner superconducting dipole is energized, currents are induced in the screen and the dipole follows, with some gliding the screen's motion, emf are then induced in the stationary windings of the stator 2 from which electrical power can be taken out. The superconducting (Nb Ti) dipole is continuously fed with two phase helium at 4.2 K and the~flow rate of evaporated gas is measured through a flowmeter. The level of the rotating liquid can be regulated with a valve on the transfer line. Temperatures of the rotating parts of the machine are detected and transmitted through telemetry equipment. The electrical background of the experiment consists of: a variable speed (0 - 3000 rpm) 250 kW asynchronous motor and its power supply; the cryoalternator itself; a 400 A dc power source to energize the rotor; and the electric load of the stator, a set of 10 x 18kW water cooled resistances.
IOC
>
Because of the restrictions given by the driving motor and the load, we decided to run at half synchronous speed (1500 rpm) to have the same currents in the machine, the same torques on the shafts and the same effects on the superconducting winding as in the nominal condition. Nevertheless, the magnetic fields keep their nominal values. Fig. 1 shows open circuit tests made to verify the previous results: I V = 0.35 mV. (rpm)-1 x If. Fig. 2 shows the power tests made at 1000 rpm and 1500 rpm for a field current of 225 A: this corresponds to its nominal value, the transition current of the dipole being more than 370 A. The field in the air gap between the stator and the driven screen is of 0.9 T. Losses of helium were about 18 lh -l during the 3 h of the power tests. The temperature of the current leads of the dipole is maintained at "x, 0°C, and the radiation shield, cooled with the recuperated He vapours is at "x, 60 K.
CRYOGENICS
. MARCH
1980
5o
--
_
Ioo
[
200
:,,A
CRTBT - CNRS, avenue des Martyrs, BP 166, 38042 Grenoble Cedex, France. YB and JM are also with the INPG (ERA 534) Paper received 30 July 1979. 0011-2275/80/003161-02
o
Fig. 1 Open circuit phase voltage variation with field currents at constant driving speedo-- 1500 rpm 0 -- 700 rpm $02.00
©
1 9 8 0 IPC Business Press 161
fz~ L
•
Oo
/
The maximum output power (point A) is of 151 kW (this corresponds to 300 kW at 3000 rpm). In A, the input is of 173 kW, this involves the losses of the dc-ac converter supply to the driving motor, and the losses of both machines, so it is difficult to give a good estimation of the efficiency of the cryoalternator. Further experiments are being prepared to determine this efficiency including a precise measurement of the gliding. Real armature losses will also be determined using a thermal method.
References 1 2 3
I
I
400 I, A
162
Brunet, Y., Mazuer, J., Renard, M., IEEE, Trans Mag 1 (1979) 723 Pinet,C., Brunet, Y., Electric Machines and Electromechanics, 3 (1979) 171 Pinet, C., Electric Machines and Electromechanics 1 (1979) 175
Fig. 2 Phasevoltage as a function of armature current. The field current is set a t / f = 2 2 5 A and the driving speed is 1500rpm. and 1000 rpm (0)
CRYOGENICS.
M A R C H 1980
Preliminary power tests of a superconducting alternator Y. B r u n e t , J. M a z u e r a n d M . R e n a r d
A cryoalternator project was initiated at the CNRS CRTBT four years ago. Up to now, only cryogenic and small power tests 1 have been performed on a 500 kW prototype which is built in the laboratory. EDF support made it possible to perform half full power tests on the machine
No anomalous effect appeared when the stator was loaded; during the tests, the load was changed in steps of "~ 15 kW and no perturbation was seen on the superconductor. Although the gliding between the screen and the dipole gives a complicated vectorial diagram of the machine, 3 a good approximation is given for the voltage drop when using a simple Behn Eshenburg theory with a synchronous reactance calculated with the open and short circuit tests (Xd -- 0.4 pu).
Our machine has been specially designed to reduce transient mechanical and heat loads. A thick screen is mechanically driven by a driving motor; when the inner superconducting dipole is energized, currents are induced in the screen and the dipole follows, with some gliding the screen's motion, emf are then induced in the stationary windings of the stator 2 from which electrical power can be taken out. The superconducting (Nb Ti) dipole is continuously fed with two phase helium at 4.2 K and the~flow rate of evaporated gas is measured through a flowmeter. The level of the rotating liquid can be regulated with a valve on the transfer line. Temperatures of the rotating parts of the machine are detected and transmitted through telemetry equipment. The electrical background of the experiment consists of: a variable speed (0 - 3000 rpm) 250 kW asynchronous motor and its power supply; the cryoalternator itself; a 400 A dc power source to energize the rotor; and the electric load of the stator, a set of 10 x 18kW water cooled resistances.
IOC
>
Because of the restrictions given by the driving motor and the load, we decided to run at half synchronous speed (1500 rpm) to have the same currents in the machine, the same torques on the shafts and the same effects on the superconducting winding as in the nominal condition. Nevertheless, the magnetic fields keep their nominal values. Fig. 1 shows open circuit tests made to verify the previous results: I V = 0.35 mV. (rpm)-1 x If. Fig. 2 shows the power tests made at 1000 rpm and 1500 rpm for a field current of 225 A: this corresponds to its nominal value, the transition current of the dipole being more than 370 A. The field in the air gap between the stator and the driven screen is of 0.9 T. Losses of helium were about 18 lh -l during the 3 h of the power tests. The temperature of the current leads of the dipole is maintained at "x, 0°C, and the radiation shield, cooled with the recuperated He vapours is at "x, 60 K.
CRYOGENICS
. MARCH
1980
5o
--
_
Ioo
[
200
:,,A
CRTBT - CNRS, avenue des Martyrs, BP 166, 38042 Grenoble Cedex, France. YB and JM are also with the INPG (ERA 534) Paper received 30 July 1979. 0011-2275/80/003161-02
o
Fig. 1 Open circuit phase voltage variation with field currents at constant driving speedo-- 1500 rpm 0 -- 700 rpm $02.00
©
1 9 8 0 IPC Business Press 161
fz~ L
•
Oo
/
The maximum output power (point A) is of 151 kW (this corresponds to 300 kW at 3000 rpm). In A, the input is of 173 kW, this involves the losses of the dc-ac converter supply to the driving motor, and the losses of both machines, so it is difficult to give a good estimation of the efficiency of the cryoalternator. Further experiments are being prepared to determine this efficiency including a precise measurement of the gliding. Real armature losses will also be determined using a thermal method.
References 1 2 3
I
I
400 I, A
162
Brunet, Y., Mazuer, J., Renard, M., IEEE, Trans Mag 1 (1979) 723 Pinet,C., Brunet, Y., Electric Machines and Electromechanics, 3 (1979) 171 Pinet, C., Electric Machines and Electromechanics 1 (1979) 175
Fig. 2 Phasevoltage as a function of armature current. The field current is set a t / f = 2 2 5 A and the driving speed is 1500rpm. and 1000 rpm (0)
CRYOGENICS.
M A R C H 1980