Power Protection System

Numerical relay is DSP based. Digital is microprocessor controlled.

So in essence the numerical relay doesn't need any A/D conversion?

refer

http://www.globalspec.com/reference/14859/121073/chapter-9-protective-relays-section-3-numerical-relays

The digital protective relay, or numeric relay , is a protective relay that uses a microprocessor to analyze power system voltages and currents for the purpose of detection of faults in an electric power system. General characteristics of a digital protective relay include:

• The relay applies A/D (analog-to-digital) conversion processes to the incoming voltages and currents.
• The relay analyzes the A/D converter output to extract, as a minimum, magnitude of the incoming quantity, commonly using Fourier transform concepts (RMS and some form of averaging are used in basic products). Further, the Fourier transform is commonly used to extract the signal's phase angle relative to some reference, except in the most basic applications.
• The relay is capable of applying advanced logic. It is capable of analyzing whether the relay should trip or restrain from tripping based on current and/or voltage magnitude (and angle in some applications), parameters set by the user, relay contact inputs, and in some applications, the timing and order of event sequences.
• The logic is user-configurable at a level well beyond simply changing front panel switches or moving of jumpers on a circuit board.
• The relay has some form of event recording. The event recording would include some means for the user to see the timing of key logic decisions, relay I/O (input/output) changes, and see in an oscillographic fashion at least the fundamental frequency component of the incoming AC waveform.
• The relay has an extensive collection of settings, beyond what can be entered via front panel knobs and dials, and these settings are transferred to the relay via an interface with a PC (personal computer), and this same PC interface is used to collect event reports from the relay.
• More complex digital relays will have metering and communication protocol ports, allowing the relay to become an element in a SCADA system.

Yes! In principle both are the same. It is only that ABB coined the word "Numerical Relays" - when they brought in their Digital Relays into the market.