IEEE C37.237-2018 pdf free download – IEEE Standard for Requirements for Time Tags Created by Intelligent Electronic Devices—COMTAG.
The lightning cloud at the left and transformer at the right of Figure 1 represent physical things in the power system. These may include signals being measured, events detected, status of equipment, and outputs for control or monitoring.
The bulbs in this drawing represent IED internal processing. It is very important to record a piece of information when the IED has detected an event. This standard addresses the following three event classifications:
— Physical events. These are when an IED activates a physical output or measures a physical input or somehow detects when an event actually happened and an event record is generated (see 3.1).
— Virtual or logical events. For system debugging, it is often useful to know the sequence of events (SOE) inside the IED for virtual or logical value changes. Therefore, recording these internal processing events is important (see 3.2).
— Communication-based events. These are recorded when the IED has decoded the actions received from another IED or when the IED sends a message to another IED. This can be used, for instance, to ensure that IEC 61850 GOOSE messages [B1] are sent and received within the required time limits (see 3.3). IED configuration provides settings that are used to define and select the events that will actually be recorded or transmitted (in general, generated). These events are thought to be important for some purpose by the configurator (seeAnnex B). 3.1 Physical events Physical events are measured values obtained by directly sampling physical inputs (perhaps after being converted to an electrical quantity by a transducer) or driving physical outputs, whether analog or discrete.
These events may be recorded or transmitted either in some continuous fashion (such as synchrophasor data, or sampled measured values in a process bus), or on a threshold-driven basis, when some characteristic of the signal crosses a threshold; for instance, when current exceeds a relay setting, or a status value changes (see Annex D).
3.1.1 Analog Analog events may be related to either input or output signals. Analog input signals are generally first converted to digital format (sampled values) using an analog-to-digital converter and then processed in the IED. This processing may include calculations to express the measured information as a real physical quantity, such as the voltage or current applied to the IED input terminals. The processing may include corrections for scaling, errors, and calibration offsets. The processing may include deadbands or detection of triggers, which may generate an event record. This information might also be used to calculate a derived quantity. For example, voltage and current data can be multiplied to calculate power.
Derived quantities may be further processed, in the same way as measured quantities, including detection of triggers. These derived quantities are addressed by 3.2. Analog outputs from IEDs, for example 4 mA to 20 mA values used to control the position of an actuator, can also generate events for their change in value. Data analysis can be more challenging if the data come from different IEDs at different rates (seeAnnex G).
3.1.2 Digital Digital input events are defined by the digital (status) value reaching a defined threshold, generally after a debounce period, which can be zero (none). Digital input events result from a physical input to the IED.
The threshold value of a digital input may or may not be user-programmable, but all digital inputs are basically analog inputs with signal processing (either analog, digital, or both) whose function is to detect when the applied signal has changed status (crossed the threshold) indicating either “on” or “off.” All digital inputs must have a threshold value, which is used internally to make that decision. That value is usually based upon a voltage range defined by the IED manufacturer as the “on range” and another corresponding range of voltage for the “off range.” Digital output events can be the result of an IED’s internal process (such as internal logic or commanded control from outside the IED), such as from a supervisory control and data acquisition (SCADA) master that initiates a change in state of an output of the IED. Digital outputs can include low-level (logic) signals intended for connection to another IED, as well as high-power contacts intended to control power system equipment (such as switchgear). Output events are defined as a change in the commanded state of the output. If the output has significant delay and means are provided to determine the actual state of the output, after a commanded change, another event may be defined as the actual time the state of the output changed.IEEE C37.237 pdf download