Electricity: motive power systems – Positional servo systems – With particular 'error-detecting' means
Reexamination Certificate
2001-09-10
2004-03-30
Dang, Khanh (Department: 2181)
Electricity: motive power systems
Positional servo systems
With particular 'error-detecting' means
C318S560000, C318S727000
Reexamination Certificate
active
06713984
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an operating device for driving and controlling the opening and closing of an electrical switching apparatus, such as a switch or a circuit breaker. The said switching apparatus is meant to be used in a high or a medium voltage transmission or distribution network and is thus used at voltages ranging from one kilovolt to several hundreds of kilovolts. The operating device is especially suited to operate circuit breakers of all types, e.g. gas, oil or vacuum isolated circuit breakers of the live tank or dead tank type. The present invention also relates to a medium voltage or a high voltage switching apparatus operated by an operating device of the aforementioned kind, and a method for operating a medium voltage or a high voltage switching apparatus.
BACKGROUND ART
In a power transmission or distribution network, switching apparatuses are incorporated into the network to provide automatic protection in response to abnormal load conditions or to permit opening or closing (switching) of sections of the network. The switching apparatus may therefore be called upon to perform a number of different operations such as interruption of terminal faults or short line faults, interruption of small inductive currents, interruption of capacitive currents, out-of-phase switching or no-load switching, all of which operations are well known to a person skilled in the art.
In switching apparatuses the actual opening or closing operation is carried out by two contacts where normally one is stationary and the other is mobile. The mobile contact is operated by an operating device which comprises an actuator and a mechanism, where said mechanism operatively connects the actuator to the mobile contact.
Actuators of known operating devices for medium and high voltage switches and circuit breakers are of the spring operated, the hydraulic or the electromagnetic type. In the following, operating devices will be described operating a circuit breaker but similar known operating devices may also operate switches.
The spring operated actuator generally uses two springs for operating the circuit breaker; an opening spring for opening the circuit breaker and a closing spring for closing the circuit breaker and re-loading the opening spring. The closing spring is recharged by an electrical motor which is situated in the operating device. A mechanism converts the motion of the springs into a translation movement of the mobile contact. In its closed position in a network the mobile contact and the stationary contact of the circuit breaker are in contact with each other and the opening spring and the closing spring of the operating device are charged. Upon an opening command the opening spring opens the circuit breaker, separating the contacts. Upon a closing command the closing spring closes the circuit breaker and, at the same time, charges the opening spring. The opening spring is now ready to perform a second opening operation if necessary. When the closing spring has closed the circuit breaker, the electrical motor in the operating device recharges the closing spring. This recharging operation takes several seconds.
Although carrying out the task for which they are deigned, spring operated operating devices have several drawbacks. The movement of the mobile contact is exclusively determined by the characteristic of the opening and closing springs and the operating mechanism. Therefore, the distance travelled by the mobile contact as a function of time, i.e. the motion profile according to which the mobile contact moves, cannot be changed by the user, as it is established upon designing the operating device. This means that once the opening or closing spring is released, the mobile contact will follow a predetermined motion profile. In addition, the energy that is supplied to the mobile contact by the actuator is established upon designing the operating device. Therefore it is not possible to adapt the motion of the mobile contact to the type of opening or closing operation that need to be performed. Nor is it possible to alter the motion of the mobile contact by controlling the speed or acceleration of said contact once the opening or closing operation is commenced.
Also, due to the presence of the springs, spring operated actuators are intrinsically poor in precision since they generally comprise a large number of components. The large number of components also requires an initial adjustment of the operating device which is complex and thereby time consuming. The poor precision in positioning the mobile contact and the absence of a control of the motion of the mobile contact may further require the presence of dampers or shock-absorbers to dissipate residual kinetic energy at the end of the opening and the closing stroke and to prevent the circuit breaker from being hit upon in an uncontrolled manner. A further drawback is the high noise levels of known spring operated operating devices, which may require the provision of an acoustic insulation in the housing of the operating device in order to limit environmental impact. Owing to the high number of components, known spring operated operating devices require regular maintenance to maintain the expected behaviour of the operating device and to compensate for variations in the motion of the mobile contact due to wear and ageing of the system. A still further problem is represented by the delay time of the circuit breaker, i.e. the time lapsing between the instant when the operating command is sent to the operating device and the beginning of the movement of the mobile contact of the current breaker. Due to the high number of components the response time in known spring operated operating devices is of the order of several milliseconds (ms).
Operating devices of the hydraulic type, wherein movement of the mobile contact is accomplished by special hydraulic actuators, can partially obviate some of the inconveniences of the spring operated operating device. Nevertheless, the hydraulic operating devices have some disadvantages related to the presence of hydraulic fluids, especially due to the viscosity of the fluids being temperature-sensitive. In addition, with hydraulic operating devices there is a risk of leakage whereby the hydraulic fluids may have impact on the environment. As with spring operated operating devices, hydraulic operating devices generate high noise levels and also require regular maintenance to maintain the expected behaviour of the operating device.
In known electromagnetic operating devices, an actuating force is produced either by the Lorentz force principle or by interacting magnetic fields generated by electromagnets.
The Lorentz force states that if a current carrying conductor is placed in a magnetic field, a force will act upon the conductor. This principle is used, for example, in a voice coil actuator which is known to operate vacuum circuit breakers. Such a voice coil is described in the patent application PCT/US96/07114. The voice coil, however, has one major drawback in the fact that the length of stroke is limited. The use of a voice coil actuator is thus limited to switches and circuit breakers that require only a short stroke.
The magnetic operating device utilises one or a plurality of electromagnets to operate the mobile contact of the circuit breaker. Several designs of magnetic operating devices exist, the operating principle of which is that an electromagnet, operatively connected with the mobile contact, moves between two end positions whereby an air gap in a magnetic circuit is closed or enlarged. An example of such a device, as presented in PCT application PCT/SE96/01341, is described in the following with reference to FIG.
1
. The mobile contact of the circuit breaker is operatively connected with a rotary device
101
comprising a number of rotationally symmetrically disposed iron armatures. The rotary device
101
is arranged in an outer stationary iron core
102
. To achieve a rotary movement, operating coils
103
, that are fixed to the iron core
102
at each ar
ABB AB
Dang Khanh
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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