AECC Interconnection Requirements

AECC Design and Operating Requirements for Interconnected Facilities

In addition to the rules and standards set forth by the APSC, FERC, and NERC, AECC and its member cooperatives have certain requirements that must be met before an interconnection can be completed. These requirements are focused primarily on the details pertaining to the design, equipment, protection, and metering. Operations, operational issues, maintenance coordination, inspection, and communications are also addressed. Many of these requirements are outlined in the documentation and agreements that are a part of the interconnection process. These requirements are subject to change without notice.

All interconnections will be subject to the design requirements described below. Due to AECC’s interconnected nature with the Entergy, AEP, OG&E, and SWPA systems, AECC may require interconnecting facilities to the AECC system to adhere to the requirements of Entergy, AEP, OG&E, and SWPA as applicable. In these requirements, the appropriate Entergy, AEP, OG&E, and SWPA documents have been referenced and are subject to change without notice. Any additional requirements included in member cooperative line extension policies may also apply. Furthermore, interconnections will meet the requirements of the NERC standards, SPP Criteria, and MISO Business Practices.

Because AECC is connected to the Entergy, AEP, OG&E and SWPA transmission systems and is under their interconnection requirements, joint studies might be conducted by them as well as SPP and/or MISO in conjunction with AECC or as an independent process to determine the indirect effect that might occur due to the new connections. Where joint studies might be necessary, it is the customer’s responsibility to provide all information necessary to AECC and all affected parties needed to conduct thorough and complete studies. [NERC FAC-001R3.1 and R4.1]

At any time, it is the customer’s responsibility to notify AECC and any affected parties of any changes, modifications, or additional new facilities while in their conceptual or planning phase. This will allow the appropriate adjustments to be made to the current study process in a timely manner such as to ensure that the proposed changes do not significantly alter the effects of the original interconnection request. If the changes do result in a significant difference from the original intent, then a separate interconnection request may be required. [NERC FAC-001R3.2 and R4.2]

NERC Standard FAC-001-3R3.3 and R4.3 requires AECC (as the Transmission Owner or Applicable Generator Owner) to be responsible for confirming that new or materially modified Facilities are within a Balancing Authority Area’s (BA) metered boundaries. All AECC BES Facilities are registered in either SPP or MISO who serves as the BA. AECC is bound to the terms and conditions set for in both respective Open Access

Transmission Tariffs (OATTs). Therefore, the interconnecting customer should be aware of the following items when seeking a new or materially-modified transmission or generation Facility interconnection:

  • The interconnecting customer is responsible for coordinating and registering new or materially-modified Facilities with the appropriate BA
  • Prior to new or materially-modified Facilities energization, the interconnecting customer must provide documented evidence of the appropriate BA registration
  • AECC will provide contact information for the appropriate BA upon request
  • AECC will provide assistance upon request
  • [NERC FAC-001R3.3 and R4.3]

In addition, AECC may require the following:

  • Any entity connecting to AECC-owned transmission lines or substations shall as a minimum meet the requirements of the National Electrical Safety Code at the time of installation and employ good utility practices when designing their facilities – AECC, at its sole discretion, may refuse interconnection of any requesting entity should the proposed design not exhibit good utility practice
  • Facility designs shall be submitted to AECC preferably with the interconnection request. AECC will review and provide comments of facility designs before construction begins
  • AECC will review interconnection facility designs on a case-by-case basis to determine appropriate levels of protection and control for the interconnection facility
  • Interconnecting facilities which may impact power quality, such as contributing harmonics and/or flicker, will be required to mitigate such impacts and control them within limits established by AECC
  • All interconnecting facilities will be designed and constructed utilizing utility-grade equipment which may include but are not limited to, utility-grade relaying, breakers, switches, metering, grounding, and controls
  • If any interconnecting customer should fail to maintain its lines, equipment, and other facilities in accordance to standards and prudent utility practices AECC shall have the right to discontinue receipt of electric power to the facilities in question after giving notice of its intention to do so
  • AECC may require the requestor to meet certain requirements in areas listed below – These requirements unless otherwise documented will be required on a case-by-case basis and discussed with the requestor before the interconnection request is approved
    • Voltage level, MW and MVAR capacity or demand at the point of interconnection
    • Interconnections that result in voltages below 95% of nominal or above 105% of nominal on AECC or its member cooperatives’ facilities will not be allowed – If an interconnection is expected to cause voltages outside the range specified above, adjustments to the interconnection will need to be made in order to bring the voltage within this range
    • Customer will provide MW, MVAR, and Demand – AECC will evaluate and determine if the point of interconnection is capable of performing the requirements
  • Breaker duty & surge protection
    • Circuit breaker duty and design criteria are found in the table below – Certain interconnections may require higher interrupting and/or continuous current ratings.
    • Surge protection devices will be installed on the interconnecting customer’s facilities such that they eliminate or sufficiently reduce the likelihood of damage to AECC’s and its member cooperatives’ facilities due to voltage surges – Surge arresters shall be station class and have voltage ratings for grounded circuits as follows:
      • 60 kilovolts (kV) for 69 kV systems
      • 96 kV for 115 kV systems
      • 108 kV for 138 kV systems
      • 132 kV for 161 kV systems

Circuit Breaker Design Criteria

  • kV = kilovolt
  • A = ampere
  • kA = kiloampere
Minimum Design Criteria Units Breaker Voltage
69 kV 115 kV 138 kV 161 kV
Max L-L voltage kV 72 123 145 170
Nominal L-L voltage kV 69 115 138 161
Continuous Current A 1200 2000 2000 2000
Short Circuit Interrupt kA 40 40 40 40
Bushing BIL kV 350 550 650 750
Max Interrupt Time Cycles 5 3 3 3
Duty Cycle 0 – 0.3 seconds – CO – 15 seconds – CO
  • The switching of loads, motors, capacitors, etc. shall not cause excessive voltage surges to occur on the AECC/Member Cooperative system. The point at which a switching surge is considered excessive shall be considered on a case-by-case basis considering the equipment that is affected. Switching surges may also be referred to as transients or voltage transients.

System Protection & Coordination

  • The interconnecting customer shall submit a single line diagram of the proposed interconnection’s protective relaying design for review by AECC before such equipment is installed. AECC will review the user’s plans for these protective devices to ensure that they are adequate – AECC’s review does not imply that the user’s protective devices meet the requirements of Other Applicable Standards
  • The interconnecting customer shall provide relay data and settings to AECC for coordination study purposes
  • For generation facilities operated in parallel with Coop Facilities, the user must provide protective devices capable of sensing a problem on Coop Facilities and disconnecting the generator from Coop Facilities. The following will also apply:
    • For generation facilities operated in parallel with Coop Facilities, the user will ensure that the generator is disconnected from Coop Facilities if an islanding event occurs (i.e. the generator is connected to an island of load which is not connected to the bulk electric system) unless other arrangements have been made with AECC and its member cooperatives
    • For generation facilities operated in parallel with Coop Facilities, the user will ensure that the user’s protective devices do not reclose the generator into the Coop Facilities until after AECC’s or its member cooperatives’ protective devices or personnel have removed any problems from the Coop Facilities
  • AECC will not be responsible for the protection of the interconnecting customer’s equipment and facility – The interconnecting customer is solely responsible for protecting their equipment in such a manner that faults, unbalances or other system disturbances on AECC’s transmission system do not cause damage to the interconnecting party’s facilities
  • Synchronizing of interconnecting facilities is the responsibility of the interconnecting customer

Metering & Telecommunications

  • Unless otherwise agreed by the parties, AECC shall install the metering equipment at the interconnecting customer’s facilities and shall own, operate, test and maintain such equipment – Metering equipment will include current transformers, potential transformers, revenue meter and accessories
  • In addition to metering, the user will supply AECC and/or its member cooperatives with a status signal indicating when the interconnected facility is connected to AECC’s or its member cooperatives’ transmission system (i.e. breaker status)
  • AECC, at its own discretion, shall install, own, operate, and maintain a remote terminal unit – Data protocol requirements for this RTU will be specified by AECC
  • Each individual party shall be responsible for installing and maintaining their own communication circuits

Grounding & Safety Issues

  • Grounding practices shall conform to applicable sections of the latest edition of the National Electric Code (NEC), National Electrical Safety Code (NESC), IEEE 80 , Guide for Safety in AC Substation Grounding, IEEE 81, Guide for Measuring Earth Resistivity, IEEE Std. 142, Industrial and Commercial Power System Grounding (Green Book), and IEEE Std. 1100, Powering and Grounding of Sensitive Equipment (Emerald Book)
  • Interconnecting customer shall design the grounding system to protect personnel and equipment during faults – All substation equipment, fencing, buildings, cabinets and structures shall be connected to the ground grid
  • Underground connections shall be exothermic type – AECC reserves the right to inspect these connections before backfilling has occurred
  • AECC will make the final determination as to whether the AECC facilities are properly protected before an interconnecting party’s facility is energized – The interconnecting customer is responsible for the adequate protections of their own equipment and for correcting such problems before the facilities are energized
  • Overhead shield wires or masts shall be installed for protection against direct lightning strikes – The shield system shall be connected to the substation ground grid – The lightning protection design shall be in accordance with IEEE 998

Insulation & Insulation Coordination

  • Power system equipment is designed to withstand voltage stresses associated with expected operation – The following ratings shall apply to the interconnecting facilities equipment and accessories
Voltage Rating Minimum Basic Impulse Level
69 kV 350 kV
115 kV 550 kV
138 kV 650 V
161 kV 750 kV

Voltage, Reactive Power, & Power Factor Control

  • When not generating or for load interconnections, the user’s facilities will maintain a 98% lagging power factor or better at the point of interconnection of its facilities with Coop Facilities during the summer months (June through September) and a 95% lagging power factor or better during all other months (October through May)
  • The interconnecting customer shall be responsible for supplying their own reactive power needs – Switched reactive resources shall be designed to not cause voltage transients on the system

Power Quality Impacts

  • Interconnecting facilities will comply with the requirements of AECC’s current Voltage Fluctuation and Harmonic Distortion Rider (VF-1) filed with the Arkansas Public Service Commission – This rider specifies the allowable voltage fluctuations and harmonic distortion allowed for interconnecting facilities

Equipment Rating

  • All power system equipment shall be designed for reliable operations
  • Equipment ratings shall be in accordance with the latest ANSI, IEEE, NEMA, and NERC requirements
  • Equipment which AECC determines unacceptable with regard to industry standards and good utility practices shall not be installed

Synchronizing of Facilities

  • Generating facilities which will be connected to Coop Facilities after they are already generating will not connect to Coop Facilities unless the Coop Facilities and the generator have a slip frequency less than 0.048 Hz and a phase angle difference of less than 40º

Maintenance Coordination

  • AECC and the interconnecting customer shall maintain their own facilities and equipment using safe, sound, and reliable utility practices
  • The interconnecting customer will coordinate all outages of its facilities with AECC prior to them being taken out of service

Operational Issues (Abnormal Frequency & Voltages)

  • Interconnecting customers connecting to AECC’s or its member cooperatives’ transmission system within the area where Entergy acts as the Transmission Provider will not create a normally closed-loop/path between two of AECC’s or its member cooperatives’ delivery points from Entergy
  • The interconnecting customer shall install adequate protection or safeguards to prevent damage to AECC due to abnormal frequency and voltage excursions originating at the interconnected facility
  • The interconnecting customer shall be required to participate in the automatic under frequency load shedding program

Inspection Requirements for Existing or New Facilities

  • Customer will provide AECC with copies of facility commissioning, inspection, and test reports
  • AECC reserves the right to inspect the interconnecting facilities prior to them being put in service – Also, after the interconnecting facilities have been put in service, AECC reserves the right to inspect them upon reasonable notification to the interconnecting customer
  • The interconnecting customer shall give advanced notice to AECC of any significant changes planned for the facility – AECC reserves the right to inspect the interconnecting facilities once these significant changes have been made by the interconnecting customer

Communications & Procedures During Normal & Emergency Operating Conditions

  • In emergency cases only, authorized personnel from AECC and its member cooperatives must have access to and permission to operate the first air break disconnect switch at the point of connection with Coop Facilities – AECC or its member cooperative shall notify the designated interconnecting customer’s representative as soon as reasonably possible after such operation, giving details as to the necessity and time of operation
  • The interconnecting customer shall notify the AECC Transmission Operations Center of normal and emergency system operational events
  • Normal events will include, but are not limited to, the following: System paralleling or splitting, scheduled and unscheduled outages, equipment clearances, etc.
  • Emergency events will include but are not limited to, the following: System events that can jeopardize the safety and reliability of AECC’s transmission system unless immediate action is taken to prevent its occurrence

Note: Unless otherwise noted, requirements for AEP will be referenced from AEP’s Requirements for Connection of New Facilities or Changes to Existing Facilities Connected to the AEP Transmission System, TP-001 latest revision.

Revision History

Version Date Reviewers Revision Description
0 5/10/2007 Ronnie Frizzell Original
1 6/1/2009 David McRae Provided additional details
2 9/15/2011 David McRae Included OG&E
3 11/15/2013 David McRae New Standard Version
4 9/11/2015 David McRae New Standard Version
5 11/28/2017 David McRae Review
6 12/17/2018 David McRae New Standard Version