SEPAM series 80 with MES120 Normally Closed Input trips upon loss of supply power

Goals and Symptoms

Symptom

• Configuration: Sepam series 80 using a MES120 digital input set as tripping order and normally closed contact (negative case is ticked off )
• Sepam trips when the auxiliary power supply is interrupted.
• After clearing the trip on Sepam, the Sepam units come to normal operating conditions without changing the state of the input.

Facts and Changes

Key Words and Phrases
Input state change from loss of supply power, loss of supply power triggers state change,ride-through power, delayed power loss, delayed power cycle

Causes and Fixes

Cause
This will append when digital inputs and Sepam base unit share the same power supply.
Because the Sepam unit has enough ride-through energy reserved to allow for momentary outages of up to 100ms without power cycling, the Sepam will detect the logical input falling down to zero due to power loss before losing its own energization. This functioning is quite normal if no precautions are taken to prevent it.

Note: Sepam series 20 and 40 don't show that behavior because they have a faster shutdown.


Resolution

As a precaution against this behavior, it is suggested to :

- if the application makes it possible, delay the tripping of normally closed contact inputs via logical equation for 200ms

- if delay is not applicable, use another input as "presence of voltage" and combine it with the logical equation.

For example :
I105 = external trip NC
I106 = presence of voltage
equations: LATCH VL1 (optional)
V1 = I105 AND I106
V_TRIPCB = V1
Link a message like "external trip" to V1

- Otherwise, to avoid trip at voluntary shut down, add a warning near the auxiliary circuit breaker.

__________________________________________________________________________________________________________

Re-published to revised security level: 20 June 2008 by DRM

Applies To: Sepam 80

Public

All content © 1992-2008 Schneider Electric

---

Legacy KB System (APS) Data: RESL177113 V2.0, Originally authored by KBAdPM on 11/05/2007, Last Edited by DaMi on 06/21/2008
Related ranges: Sepam series 80