IEEE Std C62.72a-2020 pdf download

IEEE Std C62.72a-2020 pdf download.IEEE Guide for the Application of Surge-Protective Devices for Useon the Load Side of Service Equipmentin Low-Voltage (1000 V or Less,50 Hz or 60 Hz)AC Power Circuits Amendment 1: SPD Disconnector Application Considerations and Coordination.
Annex F
(informative)
SPD disconnectors
Insert Aniiex F after Annex E.
F.1 Operational characteristics of SPD disconnectors
This clause includes the identification of various disconnector types and their operating characteristics.
F.1.1 Thermal disconnectors used in SPDs
F.1.1.1 Eutectic alloy solder pot
A thermally sensitive solder in a cylindrical pot.
F.1.1.2 Melting alloy thermal relay
A melting alloy thermal relay, also called a cutectic alloy solder pot relay, consists of a rotating spindle that is initially placed in a container of molten solder, which is then solidified by cooling to constrain the spindle from rotating. Note that this device is typically resettable. For use as a disconnector for a surge- protective device (SPD), the melting alloy relay is placed in close proximity to the metal oxide varistor (MOV). The spindle is connected to a switch that opens or disconnects the MOV when the spindle rotates. When the MOV begins to heat tip due to overvoltage or some other fault, the heat transfers to the melting alloy relay and disconnects the circuit.
F.1 .1.3 Thermal fuse spring (thermal disconnector fuse spring)
A thermal disconnector fuse—spring may be defined as a heat-sensitive component that is under tension/compression force and is designed to operate at a specified temperature to create an electrical isolation by means of a separation distance. This is usually a combination of a metal disconnecting element and eutectic solder (free standing versus pot type).
F.1.1.4 Bi-metal device
A bi-metal thermal relay consists of two dissimilar metal strips fastened together at the ends. These metals expand at different rates when subjected to heat resulting is a bowing action of the strip assembly. Note that this device is typically resettable. The bimetal strip is placed in close proximity to the heat-generating surge-protective components (SPCs) (e.g., MOV). This device can be used in series with the SPC. When the heat-generating SPC begins to heat tip due to overvoltage or some other fault, the heat transfers to the bimetal strip causing the strip to deform or curve toward or away from the heat source. The bi-metal strip will then either trip a micro-switch or otherwise disconnect the over-heated SPC or the SPD.
F.1.1.5 Positive temperature coefficient (PTC) devices
F.1.1.5.1 Polymer PTC (PPTC) thermistor
The PPTC thermistor is made of polymeric materials with very low resistance. When heated (i.e., due to an over-current event), the resistance will increase to reduce the current flow. Once an ovcrcurrcnt condition is removed (and the device cooled down), the materials return to its low resistance state.
F.1.1.5.2 Ceramic PTC (CPTC) thermistor
The CPTC thermistors are thermally sensitive semiconductors made of a doped polycrystalline ceramic containing materials that exhibit an increase in resistance at a specified temperature. When heated (overcurrent event), the dielectric constant allows the formation of potential barriers at the grain boundaries, and the resistance increases. Once a circuit fault is removed (and the device has cooled), the device returns to its low resistance state.
F.1 .1.6 Thermal cutoff (TCO)
A TCO is an electrical supplemental protection device that internlpts electric current when heated to a specific temperature.
F.1 .2 Electronic trip disconnectors
Electronic trip disconnectors are those devices that can sense and open the circuit path of an SPC or an SPD when subjected to overcurrent, overvoltage, over temperature, or other predefined fault conditions. Electronic trip disconnectors can be used in conjunction with other disconnectors to provide these functions.
An example of an electronic trip disconnector is shown in Figure F. I. In Figure F. 1, the electronic trip disconnector includes a power supply circuit, sense circuits, a control circuit, and a circuit breaker as a disconnector. Electronic trip disconnectors can be more simplistic or more complicated based on design and functionality requirements.
NOTE—The power supply that powers the sensing electronics may only work down to a certain lower voltage level unless an alternative, ancillary power source is provided.