Patent Description:
In many cases, an electric power system comprises elements such as generators, electric machines, and power converters. Furthermore, an electric power system may comprise protector elements such as for example over-current protectors, over-voltage protectors, under-voltage protectors, and overheating protectors. For example, an over-current protector can be e.g. a fuse or a relay configured to break an electric circuit when current gets dangerously strong. For another example, an overheating protector may comprise one or more temperature sensors and a relay configured to switch off power supply when one or more measured temperatures get dangerously high.

After a fault or another problem has occurred in an electric power system, it can be important to analyze the problem in order to see how the electric power system should be modified and/or used so that similar problems can be avoided in the future. In order to provide data for the analysis, an electric power system can be provided with recording devices which are located at different elements of the electric power system and which are configured to record waveform samples of quantities related to the operation of these elements. The quantities may comprise for example currents, voltages, and/or temperatures measured from the elements of the electric power system. The electric power system may further comprise a central device communicatively connected to the recording devices and configured to receive the recorded waveform samples from the recording devices. The recorded waveform samples may serve as analysis data based on which the operation of the electric power system prior to an occurrence of a fault or another problem can be analyzed. For example, recorded waveform samples of currents and voltages may reveal that a fault was preceded by sudden drops in particular voltages and/or sudden increases in particular currents. In many situations, it can be however challenging to identify which of phenomena, such as e.g. abrupt changes in currents and/or voltages, indicated by recorded waveform samples are causes and which of the phenomena are, in turn, consequences.

Publication <CIT> describes a protection system for protecting monitored equipment at both a local level and a system level, to provide comprehensive protection. The protected equipment may comprise for example one or more generators. The protection system may utilize time-synchronized data to analyze data provided by systems having disparate sampling rates, which are monitored by different equipment and/or by equipment that is geographically separated.

Publication <CIT> describes a power diagnostic system for detecting faults. The system comprises a processor coupled to a plurality of sampling blocks which simultaneously perform current measurements and voltage measurements at a plurality of loads based on a reference signal generated by a clock generator. The sampling blocks measurements are sent to the processor via power cables that are also used to supply power to the plurality of loads. The sampled currents and voltages are compared to threshold values, and faults are identified if the sampled currents and voltages vary from the threshold values.

Publication <CIT> describes an intelligent electronic device configured to detect a transient traveling wave caused by an electrical fault. A first value of the transient traveling wave may be determined and a corresponding first time associated with the first value may be determined. A second time associated with a second value corresponding to the first value of the transient traveling wave is detected by a remote device. The distance to the remote device is known. An estimated fault location may be generated based on the time difference between the first time and the second time.

The following presents a simplified summary in order to provide a basic understanding of some aspects of various invention embodiments.

In accordance with the invention, there is provided an electric power system according to claim <NUM>.

The central device which is configured to receive the recorded waveform samples provided with the timing values can be a separate device with respect to the recording devices, or the central device and one of the recording devices can be implemented as a single apparatus.

As the timing values are associated to the waveform samples, it is possible to identify the temporal order of phenomena, such as e.g. abrupt changes in currents and/or voltages, indicated by the recorded waveform samples. Thus, it is possible to identify which of the phenomena are causes and which are, in turn, consequences when analyzing for example what happened prior to a fault situation.

In accordance with the invention, there is provided also a method for monitoring an electric power system according to claim <NUM>.

A method according to an exemplifying and non-limiting embodiment of the invention further comprises identifying, based on the timing values associated to the recorded waveform samples, the temporal order of phenomena indicated by the recorded waveform samples.

A number of exemplifying and non-limiting embodiments of the invention are described in accompanied dependent claims.

The verbs "to comprise" and "to include" are used in this document as open limitations that neither exclude nor require the existence of un-recited features.

Exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below in the sense of examples and with reference to the accompanying drawings, in which:.

The specific examples provided in the description below should not be construed as limiting the scope and/or the applicability of the accompanied claims. Lists and groups of examples provided in the description are not exhaustive unless otherwise explicitly stated.

<FIG> shows a schematic illustration of an electric power system according to an exemplifying and non-limiting embodiment of the invention. In this exemplifying case, the electric power system is a part of an electric system of a ship or a ferry.

The electric power system comprises a generator <NUM> driven with a combustion engine <NUM> that can be for example a diesel engine. The electric power system comprises electric machines <NUM> and <NUM> for driving actuators. In this exemplifying case, the actuators are propellers. Furthermore, the electric power system may comprise e.g. a lighting system <NUM>. The electric power system comprises a power control system for transferring electric power from the generator <NUM> to the electric machines <NUM> and <NUM> and to other power consuming loads of the electric power system. In this exemplifying case, the power control system comprises a direct voltage rail <NUM>, a first power converter <NUM> for transferring electric energy from the generator <NUM> to the direct voltage rail <NUM>, and second power converters <NUM> and <NUM> for converting the direct voltage UDC of the direct voltage rail <NUM> into voltages suitable for the electric machines <NUM> and <NUM>. The power control system further comprises a battery element <NUM> and a third power converter <NUM> for transferring electric energy between the direct voltage rail <NUM> and the battery element <NUM>. Furthermore, the power control system comprises a power converter <NUM> for converting the direct voltage UDC of the direct voltage rail <NUM> into voltages suitable for the lighting system <NUM>, and a power converter <NUM> for receiving electric power from a shore-side power distribution grid <NUM>.

The electric power system comprises recording devices <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> located at different sites of the electric power system and configured to record waveform samples of quantities related to operation of elements of the electric power system. The quantities may comprise for example currents, voltages, and/or temperatures measured from the elements of the electric power system. <FIG> shows an exemplifying waveform sample <NUM> of the current iG of one phase of the generator <NUM> and an exemplifying waveform sample <NUM> of the direct voltage UDC of the direct voltage rail <NUM>. The electric power system comprises a central device <NUM> which is communicatively connected to the recording devices <NUM>-<NUM> and which is configured to receive the recorded waveform samples from the recording devices. The recording devices <NUM>-<NUM> are synchronized with respect to each other to maintain a clock time that is common to the recording devices <NUM>-<NUM>. The recording devices are configured to associate, to each of the recorded waveform samples, timing values indicative of the clock time during recording the waveform sample under consideration. In the exemplifying case illustrated in <FIG>, the timing values t<NUM> and t<NUM> corresponding to the beginning and the end of the waveform sample <NUM> are associated to the waveform sample <NUM>. Correspondingly, the timing values t<NUM> and t<NUM> corresponding to the beginning and the end of the waveform sample <NUM> are associated to the waveform sample <NUM>.

As the timing values are associated to the waveform samples, it is possible to identify the temporal order of phenomena, such as e.g. abrupt changes in currents and/or voltages, indicated by the recorded waveform samples. Thus, it is possible to identify which of the phenomena are causes and which are, in turn, consequences when analyzing for example what happened prior to a fault situation. A part <NUM> of <FIG> shows the exemplifying waveform samples <NUM> and <NUM> on a same time axis. The positions of the waveform samples <NUM> and <NUM> on the time axis can be determined with the aid of the timing values t<NUM>, t<NUM>, t<NUM>, and t<NUM>. In this exemplifying case, one can see that the drop in the direct voltage UDC of the direct voltage rail <NUM> takes place prior to the sudden increase in the generator current iG.

In an electric power system according to an exemplifying and non-limiting embodiment of the invention, the central device <NUM> is configured to control, based on the timing values associated to the recorded waveform samples, a display screen <NUM> to display the recorded waveform samples on a same time axis. The display screen <NUM> can be controlled to display the recorded waveform samples for example in the way illustrated in the part <NUM> of <FIG>.

In an electric power system according to an exemplifying and non-limiting embodiment of the invention, the recording devices <NUM>-<NUM> are configured to record the waveform samples according to a continuous loop recording mode where new data is recorded by overwriting corresponding old data which has been recorded a predetermined amount of time earlier. The predetermined amount of time corresponds to the temporal length of a recorded waveform sample.

In an electric power system according to an exemplifying and non-limiting embodiment of the invention, one or more of the recording devices <NUM>-<NUM> are configured to detect one or more predefined events which may occur within the electric power system. Furthermore, the one or more of the recording devices <NUM>-<NUM> can be configured to send, to the central device <NUM>, an event indicator identifying a detected event and expressing the clock time at a moment of detection of the event. In exemplifying cases where the waveform samples are recorded according to the above-mentioned continuous loop recording mode, the recording of each waveform sample can be continued after a detected event for a predetermined time period that is shorter than the temporal length of the recorded waveform sample. Thus, each recorded waveform sample contains a first portion recorded prior to the detected event as well as a second portion recorded after the detected event.

The events capable of being detected may comprise for example an activation of an over-current protector e.g. a blowout of a fuse, an activation of an over-voltage protector, an activation of an under-voltage protector, and/or an activation of an overheating protector. For example, the recording device <NUM> can be configured to detect a blowout of a fuse <NUM> and/or to detect over- and under-voltage situations which may take place on the direct voltage rail <NUM>. For another example, the recording device <NUM> can be configured to detect over-current situations of the generator <NUM> and/or to detect over- and under-voltage situations of the generator <NUM> and/or to detect overheating situations of the generator <NUM>.

In an electric power system according to an exemplifying and non-limiting embodiment of the invention, the recording devices <NUM>-<NUM> comprise processors for maintaining the common clock time in accordance with a timing signal received from a timing source <NUM>. It is also possible that one of the recording devices <NUM>-<NUM> is a master device that acts as a timing source and the other recording devices synchronize themselves with the master device. The recording devices <NUM>-<NUM> can be configured to communicate with the timing source <NUM> and/or with each other in accordance with a packet switched communication protocol. The packet switched communication protocol can be for example the Internet Protocol "IP", the Ethernet protocol, or some other suitable packet switched communication protocol. The processors of the recording devices <NUM>-<NUM> can be configured to maintain the clock time in accordance with a timing protocol suitable for packet switched data networks. The timing protocol can be for example the IEEE <NUM> time distribution protocol where "IEEE" is the acronym of the Institute of Electrical and Electronics Engineers.

The central device <NUM> and the recording devices <NUM>-<NUM> can be implemented with appropriate sensors and with processor circuits each of which can be a programmable processor circuit provided with appropriate software, a dedicated hardware processor such as for example an application specific integrated circuit "ASIC", or a configurable hardware processor such as for example a field programmable gate array "FPGA". It is also possible that the central device <NUM> and/or the recording devices <NUM>-<NUM> are parts of the power converters <NUM>, <NUM>, and/or <NUM>.

<FIG> shows a flowchart of a method according to an exemplifying and non-limiting embodiment of the invention for monitoring an electric power system. The method comprises the following actions:.

A method according to an exemplifying and non-limiting embodiment of the invention comprises identifying, based on the timing values associated to the recorded waveform samples, a temporal order of phenomena indicated by the recorded waveform samples.

A method according to an exemplifying and non-limiting embodiment of the invention comprises controlling, based on the timing values associated to the recorded waveform samples, a display screen to display the recorded waveform samples on a same time axis.

A method according to an exemplifying and non-limiting embodiment of the invention comprises recording the waveform samples according to a loop recording mode where new data is recorded by overwriting corresponding old data recorded a predetermined amount of time earlier.

A method according to an exemplifying and non-limiting embodiment of the invention comprises detecting whether any of one or more predefined events takes place within the electric power system. The method may further comprise sending, to a central device, an event indicator identifying a detected event and expressing the clock time at a moment of detection of the event. In exemplifying cases where the waveform samples are recorded according to the above-mentioned loop recording mode, the recording of each waveform sample can be continued after the detected event for a predetermined time period that is shorter than the temporal length of the recorded waveform sample. A method according to an exemplifying and non-limiting embodiment of the invention comprises detecting an activation of an over-current protector of the electric power system. A method according to an exemplifying and non-limiting embodiment of the invention comprises detecting an activation of an over-voltage protector of the electric power system. A method according to an exemplifying and non-limiting embodiment of the invention comprises detecting an activation of an under-voltage protector of the electric power system. A method according to an exemplifying and non-limiting embodiment of the invention comprises detecting an activation of an overheating protector of the electric power system.

A method according to an exemplifying and non-limiting embodiment of the invention comprises maintaining the above-mentioned clock time in accordance with a timing signal received from a timing source. A method according to an exemplifying and non-limiting embodiment of the invention comprises maintaining the clock time in accordance with a timing protocol suitable for packet switched data networks.

In a method according to an exemplifying and non-limiting embodiment of the invention, the electric power system comprises one or more generators, one or more electric machines for driving actuators, and a power control system for transferring electric power from the one or more generators to the one or more electric machines.

In a method according to an exemplifying and non-limiting embodiment of the invention, the above-mentioned power control system comprises a direct voltage rail, one or more first power converters for transferring electric energy from the one or more generators to the direct voltage rail, and one or more second power converters for converting direct voltage of the direct voltage rail into voltages suitable for the one or more electric machines. In a method according to an exemplifying and non-limiting embodiment of the invention, the above-mentioned power control system comprises one or more battery elements and one or more third power converters for transferring electric energy between the direct voltage rail and the one or more battery elements.

Claim 1:
An electric power system comprising:
- recording devices (<NUM>-<NUM>) located at different elements of the electric power system and configured to record waveform samples (<NUM>, <NUM>) of quantities related to operation of the elements of the electric power system, and
- a central device (<NUM>) communicatively connected to the recording devices and configured to receive the recorded waveform samples from the recording devices,
wherein:
- the recording devices are synchronized with respect to each other to maintain a clock time common to the recording devices, and
- the recording devices are configured to associate, to each of the recorded waveform samples, timing values indicative of the clock time during recording the waveform sample under consideration, one of the timing values corresponding to a beginning of the waveform sample and another one of the timing values corresponding to an end of the waveform sample, and timing values corresponding to the beginning and the end of one of the recorded waveform samples being a current waveform sample (<NUM>) and timing values corresponding to the beginning and the end of another one of the recorded waveform samples being a voltage waveform sample (<NUM>) are different from each other, respectively, and the one of the recorded waveform samples and the other one of the recorded waveform samples are partially overlapping in time.