S&C Develops a Cost-Effective Protection Scheme for a New Waste Water Treatment Plant.

A utility in the northeastern United States required a protection system for their substation at a new waste treatment plant. The utility was familiar with S&C’s High Reliability Distribution System implemented at International Drive, Orlando, Florida, for Florida Power Corp. and in turn, approached S&C to provide the protection scheme for their new system.

S&C engineers consulted with the local utility providing a cost/benefit analysis of several reliability options. The outcome of this discussion challenged S&C to develop a cost-effective and reliable protection solution implementing the following utility requirements:

Relaying

Directional and non-directional overcurrent
Overvoltage (phase, zero sequence, and/or phase)
Live-line closing
Auto-close lockout reset
Remote operations lockout on low pressure indication
Local/remote operations

Communication and annunciator

Interrupter/switch position and trip indication
Low-pressure alarm
Local/remote indication
Battery charger alarms

S&C’s one-line for this installation is shown below.

One-line diagram.

The incoming feed to the waste water treatment facility is served though a feeder bus connected to two 4.16-kV delta-wye transformer banks via two incoming 23-kV feeder lines. S&C’s Vista® Underground Distribution Switchgear was installed on the high-side of each transformer bank providing source, branch, and tie protection. Each Vista switchgear has one SEL-351 relay. The S&C SC-1000 microprocessor-based relay was also considered for tie and branch protection.

S&C engineers considered all possible fault scenarios in the substation and developed the relaying protection scheme according to the mandated design requirements. Faults are isolated from feeding points by Vista ways and utility breakers, which are located on the source side and branch side. In addition to the design criteria set forth by the utility, S&C provided an enhanced set of features to take full advantage of the newly developed protection scheme. Relays were programmed to handle faults through logical schemes and peer-to-peer communication. Peer-to-peer relay communication allows the SEL-351 to give or remove permission for its partner relay to operate. This insures that under certain operating conditions, a fault will be cleared successfully by the action of both relays.

S&C was fully responsible for the design phase of the project including:

Project Management
Protection and coordination studies
Equipment procurement
Programming
Factory acceptance testing
Drawing package and documentation
Training
Field support
Warranty support

The utility has since implemented the complete system and has conducted several successful tests to ensure the viability of S&C’s design.

From the initial study, to system design, to project implementation, S&C’s core expertise in electric power switching and protection enables us to provide the most comprehensive system reliability package to meet each customer’s specific requirements for their system.