As Khan tells you, the -ed forms you ask about are not being used as past-tense forms but as past participles.
With "regular" verbs, the past-tense and past-participle forms are the same. But many of the oldest verbs in the language follow different patterns, in which the past-participle form is marked with a change in the stem vowel or an -en ending, or both.
PLAIN FORM PAST FORM PAST PARTICIPLE
sing sang sung
break broke broken
give gave given
It is the past-participle form which combines with a form of BE to form the passive-voice construction. The participle itself has no tense; the time referred to is determined by the tense of the BE form:
ACTIVE VOICE: Somebody punishes Pierre. Somebody punished Pierre.
PASSIVE VOICE: Pierre is punished. Pierre was punished.
ACTIVE VOICE: Somebody sings a song. Somebody sang a song.
PASSIVE VOICE: A song is sung. A song was sung.
The past-participle form also combines with a form of HAVE to form the perfect construction; and the perfect and passive may be combined with the past-participle form of BE:
PRESENT PERFECT PAST PERFECT
ACTIVE VOICE: Somebody has punished Pierre. Somebody had punished Pierre.
PASSIVE VOICE: Pierre has been punished. Pierre had been punished.
ACTIVE VOICE: Somebody has sung a song. Somebody had sung a song.
PASSIVE VOICE: A song has been sung. A song had been sung.
All of these may also be cast into future tense with the modal auxiliary will or the BE going to construction. In this case the following auxiliary ('helping') verb, BE or HAVE, takes the infinitive form
ACTIVE: Somebody will sing a song. Somebody is going to sing a song
PASSIVE: A song will be sung. A song is going to be sung.
PERFECT ACTIVE: Somebody will have sung a song. Somebody is going to have sung a song.
PERFECT PASSIVE: A song will have been sung. A song is going to have been sung.
There's rarely a need for the future perfect; I've seen an estimate that the future perfect passive occurs about once every 1800 printed pages!