RU2028633C1 - Method of measurement of capacitance relative to frame of ship power system - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: method of measurement of capacitance of ship power plant relative to frame refers mainly to ship high-voltage system. It uses A. C. bridge and consists in de-energizing of system, in switching on of communicational gears, in check of lack of resistance coupling to frame, in inter shorting of three phases of main distribution board. After this A. C. bridge is placed between any convenient point of current carrying parts of system and frame and summary capacitance of system relative to frame is measured. EFFECT: enhanced precision of measurements, reduced labour input into measurement process.

Description

 The invention relates to electrical engineering, in particular electrical engineering, and can be used in marine electrical power systems (SEES) with a voltage above 1000 V.

 The known method of indirectly determining the capacity of the SEES relative to the hull by direct alternating circuit of the phases of the ship network to the hull according to the measured currents of single-phase faults on the hull.

 The disadvantages of this method are: an indirect method for determining capacity, requiring subsequent calculation and leading to a decrease in accuracy; the need for three-fold artificial single-phase short circuit under the operating voltage of the network is fraught with increased danger of electric shock, especially at high voltage.

 The closest in technical essence to the proposed one is the method of element-wise measurement of capacitance relative to the hull of ship’s high-voltage electric power systems, used for measuring the capacity of the 6-kV SEES of the Valentin Shashin drilling vessel, in which the three-phase capacitance is measured with an AC bridge, for example, of the P577 type the enclosures of the individual elements of the SEES (generators and consumers with the corresponding lengths of cables to the switching devices). The total capacitance of the high-voltage part of the SEES is determined by summing the measured capacitances of the elements.

 The disadvantages of this method are: reduced accuracy in determining the capacity of the SEES, caused by an indirect measurement method, requiring subsequent calculation; increased complexity associated with the need to measure the capacitances of all elements of the high-voltage SEES and subsequent calculation.

 The aim of the invention is to increase accuracy and reduce the complexity of the measurement process.

 This goal is achieved by de-energizing the SEES, turning on all switching devices, shorting the three phases of the main distribution panel (MDB), and then turning on the AC bridge between any convenient point of the current-carrying parts of the SEES and the hull and measuring the total capacity.

 Thanks to this process of performing interrelated actions, an increased accuracy of measuring the capacity of the SEES is achieved and the complexity of the measurement process is reduced.

 The essence of the proposed method lies in the fact that direct measurements of the capacitance of three phases relative to the hull of the vessel are carried out by an alternating current bridge, in a de-energized state of the SEES, i.e. with removed operating voltage.

 The methods for measuring the capacitance of electric networks associated with removing the operating voltage (disconnecting the network) did not find practical application at either low or high voltages, mainly for three reasons.

 Firstly, in the production environment (shore networks and ship voltage below 1000 V), a blackout of the network leads to an economically disadvantageous suspension for the duration of the measurement of the working process. This reason is absent in high-voltage SEPS, since the measurements can be timed to the time of the ship’s stopping, when the high-voltage part of the SEES is usually “de-energized”, and the power to the parking low-voltage consumers is provided from a low-voltage parking power station or from a coastal source.

 Secondly, the asymmetry of phase capacities characteristic of coastal networks and ship voltages up to 1000 V requires their phase-by-phase measurement, i.e. unrealistic operation of disconnecting between three phases of sources and consumers of electricity. For measuring capacitances under voltage, for example the first specified method, this is not required. The phase capacitances of the high-voltage part of the SEES are, as is well known, symmetrical, so there is no need for phase-by-phase capacitance measurements and it becomes possible to directly determine the total capacitance of the three phases. The SEES electrical safety level is determined by this total capacity, and its measurement is incomparably simpler than the capacity of each phase.

 Thirdly, for direct measurement of the total capacity of the three phases of the SEES, it will be necessary to electrically connect all its elements by artificially shorting all switching devices of the sources and consumers of electricity. For usually branched shore networks and ship voltage up to 1000 V, this is also not real. The high-voltage part of the SEES is, as a rule, low-branched. At high voltage (most often 6 kV), the most powerful consumers are fed, the number of which usually does not exceed one or two dozen. Therefore, it is not difficult to mechanically or using operative current to artificially short-circuit a limited number of switching devices.

 The inclusion of all switching devices of the high-voltage part of the SEES (circuit breakers) of disconnectors, high-voltage contactors is necessary for the electrical connection between its elements (sources, consumers, cable network), i.e. all capacity carriers.

 Verification of the absence of galvanic connections of the current-carrying parts of the SEES with the hull of the vessel is necessary because in the presence of such connections it is impossible to measure the capacitance between them and the hull by an AC bridge. The readings of the device will be zero, since the capacitance at its output will be shunted by these galvanic couplings. Verification can be done with a conventional tester.

 If the SEES was under operating voltage shortly before the capacitance measurement, then dangerous electrical charge could accumulate on live parts. Therefore, before starting the measurements, without touching the live parts, they must be discharged to the housing. This can be accomplished, for example, with a standard short circuit breaker, or using portable grounding.

 Since all elements of the SEES have an inductance, which affects the accuracy of measuring the capacitance by an AC bridge, to reduce this effect, before measuring the capacitance, the three phases of the main switchgear buses are short-circuited. This shorting is carried out in any convenient place of the main switchboard with a bare wire, under the screw to ensure reliable electrical contact.

 When turning on the AC bridge between live parts and the housing, reliable electrical contact must also be ensured. Measurements are carried out according to the instructions for use of the measuring bridge. However, in order to avoid interference-free interference, the device’s body is not grounded to the ship’s hull, which requires additional measures to ensure electrical safety: installing the device on a dielectric stand, operator being on a dielectric mat, at a safe distance from grounded structures and equipment.

 If necessary, sectional measurements of the capacitance, as well as capacities, in separate operating modes of the SEES can be performed. In these cases, when the voltage is removed, not all switching devices are closed, but only a part of them, which ensures the electrical connection of the SEES elements involved in this mode.

 This method allows to obtain a specific technical and economic effect caused by an increase in the accuracy of measurements and a decrease in their complexity. An additional significant advantage of the method, compared with measurements under operating voltage, is its safety.

Claims (1)

 METHOD FOR MEASURING CAPACITY RELATING TO SHIP OF SHIPPING ELECTRIC POWER SYSTEMS, which consists in measuring capacitance using an AC bridge when the power system is de-energized and shorting its three phases, characterized in that, in order to increase accuracy and reduce the complexity, including all switching devices and the three bus phases of the main switchboard of the electric power system are interconnected, connecting an AC bridge between any convenient part of the system and the housing, by measuring total capacitance of the three phase power system.