Project involved the installation of a 15kV switchgear with 20 vertical sections and the implementation of a secondary selective automatic transfer/retransfer scheme. The switchgear was arranged in a main-tie-tie-main configuration, with one tie in a normally open state and the other in a normally closed state. The transfer scheme was designed to trip a main breaker when its source was lost, and close the tie breaker to restore power to the affected bus. The scheme was also designed to perform a synchronized closing of the open main breaker and opening of the tie breaker, when the source that was lost was restored, which restores the system to its initial state. The scope of work for the project included:
Development of the protective relaying one-line and schematic drawings necessary for the auto-transfer scheme.
Implementation of bus protection using arc-flash-based technology.
Review/approval of switchgear manufacture drawings for the auto transfer scheme.
Development of relay files for the implementation of auto transfer and retransfer, which included three SEL-751 relays and an SEL-2100 relay communicating using Mirrored Bits.
Testing and commissioning the transfer and retransfer scheme.
Development of narratives on the operation of the transfer scheme and training the client on how to operate the new system.
480Vac Main-Tie-Generator-Tie-Main System Auto-Transfer
Project involved the implementation of a transfer scheme involving two main sources and a generator, with one normally open tie breaker and a normally closed tie breaker. Under normal operations the generator remained in the off state. When one of the main sources is lost, the affected main is tripped and the normally open tie breaker is closed to restore power to the dead bus. Furthermore, the generator is automatically started into a standby mode. If the only main source left is lost, the affected main is tripped and the generator breaker closed for the generator to supply power to both buses of the 480Vac switchgear. When one of the main sources is restored, the generator is synchronized to that main source to close the corresponding main breaker, which results in the generator returning to the standby mode. The generator ultimately transitions to the off mode after the second main source is restored. The scope of work for this project is summarized as follows:
Specifying relays for the project and reviewing/approving vendor drawings for the switchgear.
Development of schematics for the auto transfer scheme, including one-line diagram, elevation drawings and DC/AC schematics.
Programming the relays for auto-transfer, which included an SEL-2505 relay and three SEL-751 relays communicating using IEC 61850 and Mirrored Bits protocols.
Developing a transfer scheme testing plan and fully commissioning the transfer scheme.
480Vac System Coordination Study and Arc-Flash Studies
Project included the modeling of electrical equipment for an Alky unit using SKM. The objective was to perform a load flow study and to ensure the new system additions could handle the available short circuit current of the system. The project also included the coordination of the new protective relays with the existing upstream relays. The scope of the project was follows:
Developing an SKM model for the additions to the power system of the refinery.
Performing short circuit analysis to confirm the specified equipment were appropriately sized.
Determining the required settings for the adjustable breakers by performing a coordination study.
Performing arc-flash studies for the project to ensure the personnel are aware of the appropriate PPE to use.
Generating the required arc-flash labels for the entire project.
15kV Switchgear Replacement with Automatic Transfer
Project included the replacement of an existing 15kV switchgear, which required the modeling of the new protective relays and performing a coordination study to determine the settings of all the relays. The new switchgear was comprised of three mains and two tie breakers in a main-tie-main-tie-main configuration. Two of the mains were part of an automatic transfer scheme using two SEL-751 relays, one for each main, and an SEL-487B relay, which protected the tie bus zone. The SEL-487B relay also provided phase and ground overcurrent protection for the two tie breakers and the third, center main. The scope of the project included:
Updating the existing SKM model to show the new 15kV switchgear with the new relays.
Development of all settings for the project, including the corresponding TCC’s for documentation.
Generation of relay logic and relay files for the automatic transfer scheme related relays, along with 34 SEL-751 relays, which were used for the feeders, two SEL-787 relays for the transformers that fed the mains, two SEL-501 breaker failure relays and determining the set points for two Basler bus differential relays.
Development of documentation outlining the operation of the automatic scheme, including the testing checklist for commissioning.