PSM stands for Pickup Setting Multiplier. It refers to a parameter used in protective relays to set the pickup or threshold level for detecting a fault condition. The PSM is usually a ratio or multiplier applied to the nominal current setting of the relay. For example, if the relay’s nominal current setting is 100A and the PSM is set to 1.2, the relay will detect a fault condition when the current exceeds 120A (100A x 1.2).
TMS is not a standard acronym in relay terminology. However, it may be a typo or a mistaken reference to TSM (Time Setting Multiplier). TSM, in protective relays, refers to a parameter used to adjust the operating time of the relay in response to a fault condition. It is a multiplier applied to the relay’s time delay setting. For instance, if the relay is set to trip after 0.5 seconds with a TSM of 0.8, the actual tripping time would be 0.5 seconds x 0.8 = 0.4 seconds.
To calculate the Pickup Setting Multiplier (PSM), you typically divide the desired pickup setting (in terms of percentage or ratio) by the nominal setting of the relay. For example, if you want the relay to pick up at 120% of its nominal setting, and the nominal setting is 100A, the PSM would be 1.2 (120/100).
The Time Setting Multiplier (TSM) in a relay is calculated by dividing the desired time delay by the nominal time setting. For example, if you want the relay to operate with a time delay of 0.4 seconds and the nominal time setting is 0.5 seconds, the TSM would be 0.4 / 0.5 = 0.8.
These parameters (PSM and TSM) are crucial in setting up protective relays accurately to ensure they respond appropriately to fault conditions while minimizing unnecessary tripping or delays. Adjusting PSM and TSM allows engineers to customize relay settings based on specific system requirements and operating conditions, thereby enhancing the reliability and efficiency of protection schemes in electrical networks.