The event leading to the Northeast Blackout originated at the Sir Adam Beck generation complex at Kingston, Ontario (part of the Ontario Hydro System). Immediately prior to the blackout, the Hydroelectric Power Commission of Ontario was meeting a system load of approximately 6400 MW with Sir Adam Beck generating 1335 MW and with a 500 MW inflow on two tie lines with PASNY. Approximately 200 MW of the 500 MW inflow was being returned to New York via other interconnections. The Beck complex is connected with the Toronto load center via five parallel 230 kV lines. In 1963, a backup relay on one of the 230 kV lines had been set substantially below the line's rating at 375 MW in order to achieve coordination with other protection devices in the power network. On the day of the blackout, the average power flow in this line reached a level of 365 MW and at 5:16 PM, the 375 MW rating was exceeded during a fluctuation in load. This caused the line to be opened by the protective relay, resulting in the power flow to Toronto being distributed among the remaining four lines, causing each of them to be overloaded with the result that they were disconnected by their relays. Thus, within a few seconds, the 1335 MW being generated at Sir Adam Beck was isolated from its load center in Toronto. This caused the generators in the Niagara area to accelerate due to the loss of electric load and with this increase in speed came a rapid increase in power output. This power had to be distributed via the interconnections with PASNY and caused the remaining lines interconnecting Ontario and PASNY to become overloaded. Thus, the sole interconnection between Ontario at New York existed at Niagara where the Beck plant was isolated from Ontario but still connected to New York. The excess power output from the Niagara area could not be handled by the remaining lines and resulted in the stability limit opening of the two 345 kV lines
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