• Criteria Limits for Distributed Energy Resource Connections to the ACE, DPL and Pepco Distribution Systems (less than 69kV)

  • 1. Single Phase Limit
    The largest capacity single phase generator or DER (battery) operating in parallel with the gird is 100kW.  Above that size, a balanced 3 phase system is required.

    2.  Voltage Limits
    DERs are permitted to cause up to 2% voltage fluctuation at the Point of Interconnection and ½ the band width of any voltage regulator or ½ the net dead band of a capacitor bank.  DERs in maximum output, are permitted to raise feeder voltage to the ANSI or state limit whichever is more conservative.

    3. Existing Distribution Circuit Capacity Limits
    The aggregate limit of large (250 kW and over) generators running in parallel with a single, existing distribution circuit is 0.5 MWs on the 4kV, 3MWs on the 12 kV, 6 MWs on the 25 kV, and 10 MWs on the 34 kV.

    4. Express Circuit Capacity Limits
    Distributed generation installations which exceed the limit for an existing circuit require an express circuit.
    The maximum generator size for express circuits shall be:

    • 4 kV                         0.5 MW          
    • 12 – 13.8 kV            10 MWs         
    • 23 – 25 kV               10 MWs         
    • 33.26 – 34.5 kV       15 MWs

    5.  Distribution Power Transformer Limit
    The aggregate limit of large (250 kW and over) generator injection to a single distribution transformer of 22.5 MVA nameplate or larger is 10 MWs. Transformers with nameplate ratings lower than 22.5 MVA will be given lower ratings on an individual basis. If the transformer rating is significantly greater than 40 MVA it may be possible to consider a greater generation capacity.

    Adding a new transformer will be considered if there is no availability on any of the existing transformers and space is available in an existing substation. Any proposed transformers would be PHI's standard distribution transformer (37 MVA nameplate rating.)

    6.  Express Circuit Length Limit
    If there is no more injection capacity or space for an additional transformer at the closest substation, the next closest substation will be considered. The length of an express circuit is limited to 5 miles, or for the sake of the feasibility study, 3.8 straight line miles to the substation. This simplification is used because the feasibility study phase does not allow for the time and resources to examine routes in detail (including existing pole lines, easements, ROW, and environmental issues etc.)

    7. When a New Substation is Required
    If a distribution express circuit can’t be built from an existing substation for a project, it will be necessary to construct a new distribution substation with a standard ring bus design.  It will be supplied by extending existing transmission lines.  In NJ, it is the developer's responsibility to verify eligibility of this configuration for solar renewable energy certificates with New Jersey's Clean Energy Program if desired.

    All limits, given above in MWs, are subject to more detailed study to ensure feasibility.

    8.  Secondary and Spot Networks
    For the Pepco DC area
    Secondary Area Network

    • No reverse power is allowed thru the network protector, and system shall cause no network protector cycling
    • Aggregate maximum injection into an area network is 5% of the area network maximum load or 500kW, whichever is less
    • Individual DER system maximum output is 50 kW
    • Aggregate maximum on a single phase line is 20 kW
    • Aggregate maximum on any transformer in the secondary area network is 5% of the transformers peak load.  This shall be determined by mapping the closest PV systems to the network transformer and summing their output.  (This will insure that a problematic concentration doesn’t occur in one part of the area network).

    Spot Network

    • Systems will be limited to 5% of the spot network peak load or less.
    • No reverse power is allowed thru the Network Protector, and system shall cause no Network Protector cycling

    For the New Jersey (Atlantic City)
    Area Network

    • Aggregate PV Gen on the network shall not exceed 10% of minimum load or 500 kW, whichever is less.  For Atl City, the limit shall be 1,500 kW (approx minimum) x 10% = 150 kW.  This network will continue to be downsized, so this aggregate amount should not be exceeded.
    • No reverse power allowed to Network Protector
    • No conditions where Network Protector is adversely affected are allowed
    • Aggregate maximum on any transformer in the secondary area network is 5% of the transformers peak load.  This shall be determined by mapping the closest PV systems to the network transformer and summing their output.  (This will insure that a problematic concentration doesn’t occur in one part of the area network).

    For the Delaware (Wilmington) area:

    • Same as DC
    • For the Wilmington Network the aggregate maximum shall be the smaller of 5% or 50 kW. 

    For the Maryland area:

    • Same as DC

    NOTE:  To allow for more PV to be put on a secondary network, Pepco has come up with the following criteria that would accommodate larger systems that are greater than the minimum daytime load of a facility:

    • For an LVAC Spot Network there must be a minimum import limit:
      • Minimum import Limit (M.I.L) is the minimum amount of power delivered to the customer from the utility.
      • The limit is (a) 20% of day-time min load, or (b) to be determined by planner in special cases.
    • For an LVAC Grid Network there must be a maximum export limit:
      • The maximum export limit allows a customer on an LVAC grid network to export excess generation to the grid without causing reverse power to the network protectors at any time.

    The limit is equal to 80% of the export (i.e. excess) generation of the customer’s system (at the grid minimum load condition), before causing reverse power to any of the network transformers/protectors in the grid network.  The PV system/facility being evaluated is evaluated with all other active and pending generation represented in the network.

    Explanation of the Reviewed Impacts
    Voltage Fluctuation – This is a metric used to represent the DER’s impact on distribution feeder voltage. It quantifies the difference in feeder voltage between when the system is running at full output and then after the generation has been suddenly lost. Larger systems and systems connected further from a substation tend to have a higher voltage fluctuation value. If this criterion can’t be met with power factor mitigation, an impact study will be required to ensure that voltage can be maintained within applicable standards.

    Steady State High Voltage – A simulation is performed which predicts how high the voltage will rise at a point in time when energy consumption is lowest on the feeder and the DER is injecting power. The system is simulated in a normal, steady state and abnormalities are not accounted for. In some cases, steady state high voltage can be mitigated by changing settings on voltage regulation equipment.

    Reverse Power Flow – Some devices may require setting changes, a re-evaluation of their control scheme, or replacement.    The lowest daytime (9am - 3pm) load going thru the lowest loaded phase of a voltage regulator or distribution power transformer must be 20% greater than the aggregate solar output downstream of the respective equipment or mitigation is required.

    Explanation of Restricted Circuits
    Restricted Circuits – any size – Given current technology, each distribution circuit will have a limit to the amount of distributed generation that can be accommodated. When the installed generation on a circuit has reached its maximum, (generally just before the point of voltage violations), no further applications can be accepted for DER’s, regardless of size, unless the customer is willing to pay for the needed upgrades.  Potential DER owners may request, at their expense, to pay for upgrades that would allow them to install their system.  In many cases, the required upgrade costs may make an installation cost prohibitive.

    Restricted Circuits – over 250kW – Circuits which have active and/or pending generation that exceeds the amount that can be accommodated may be restricted to generators with AC ratings of 250 kW or less. Typically, this is done in the case where distributed generation requests exceed set criteria limits in order to avoid closing the circuit entirely.  (See: 3. Existing Distribution Circuit Capacity Limits)